diff --git a/modules/swagger-codegen/src/main/resources/Java/pojo.mustache b/modules/swagger-codegen/src/main/resources/Java/pojo.mustache
index 069b17ba9e..d6d6738c05 100644
--- a/modules/swagger-codegen/src/main/resources/Java/pojo.mustache
+++ b/modules/swagger-codegen/src/main/resources/Java/pojo.mustache
@@ -44,6 +44,11 @@ public class {{classname}} {{#parent}}extends {{{parent}}} {{/parent}}{{#parcela
   {{#isListContainer}}
 
   public {{classname}} add{{nameInCamelCase}}Item({{{items.datatypeWithEnum}}} {{name}}Item) {
+    {{^required}}
+    if (this.{{name}} == null) {
+      this.{{name}} = {{{defaultValue}}};
+    }
+    {{/required}}
     this.{{name}}.add({{name}}Item);
     return this;
   }
@@ -51,6 +56,11 @@ public class {{classname}} {{#parent}}extends {{{parent}}} {{/parent}}{{#parcela
   {{#isMapContainer}}
 
   public {{classname}} put{{nameInCamelCase}}Item(String key, {{{items.datatypeWithEnum}}} {{name}}Item) {
+    {{^required}}
+    if (this.{{name}} == null) {
+      this.{{name}} = {{{defaultValue}}};
+    }
+    {{/required}}
     this.{{name}}.put(key, {{name}}Item);
     return this;
   }
diff --git a/modules/swagger-codegen/src/main/resources/JavaJaxRS/pojo.mustache b/modules/swagger-codegen/src/main/resources/JavaJaxRS/pojo.mustache
index 5c0cc88526..89ce4e7dd5 100644
--- a/modules/swagger-codegen/src/main/resources/JavaJaxRS/pojo.mustache
+++ b/modules/swagger-codegen/src/main/resources/JavaJaxRS/pojo.mustache
@@ -40,6 +40,11 @@ public class {{classname}} {{#parent}}extends {{{parent}}}{{/parent}} {{#seriali
   {{#isListContainer}}
 
   public {{classname}} add{{nameInCamelCase}}Item({{{items.datatypeWithEnum}}} {{name}}Item) {
+    {{^required}}
+    if (this.{{name}} == null) {
+      this.{{name}} = {{{defaultValue}}};
+    }
+    {{/required}}
     this.{{name}}.add({{name}}Item);
     return this;
   }
@@ -47,6 +52,11 @@ public class {{classname}} {{#parent}}extends {{{parent}}}{{/parent}} {{#seriali
   {{#isMapContainer}}
 
   public {{classname}} put{{nameInCamelCase}}Item(String key, {{{items.datatypeWithEnum}}} {{name}}Item) {
+    {{^required}}
+    if (this.{{name}} == null) {
+      this.{{name}} = {{{defaultValue}}};
+    }
+    {{/required}}
     this.{{name}}.put(key, {{name}}Item);
     return this;
   }
diff --git a/modules/swagger-codegen/src/main/resources/JavaPlayFramework/pojo.mustache b/modules/swagger-codegen/src/main/resources/JavaPlayFramework/pojo.mustache
index 27ea403181..1811924571 100644
--- a/modules/swagger-codegen/src/main/resources/JavaPlayFramework/pojo.mustache
+++ b/modules/swagger-codegen/src/main/resources/JavaPlayFramework/pojo.mustache
@@ -38,6 +38,11 @@ public class {{classname}} {{#parent}}extends {{{parent}}}{{/parent}} {{#seriali
   {{#isListContainer}}
 
   public {{classname}} add{{nameInCamelCase}}Item({{{items.datatypeWithEnum}}} {{name}}Item) {
+    {{^required}}
+    if (this.{{name}} == null) {
+      this.{{name}} = {{{defaultValue}}};
+    }
+    {{/required}}
     this.{{name}}.add({{name}}Item);
     return this;
   }
@@ -45,6 +50,11 @@ public class {{classname}} {{#parent}}extends {{{parent}}}{{/parent}} {{#seriali
   {{#isMapContainer}}
 
   public {{classname}} put{{nameInCamelCase}}Item(String key, {{{items.datatypeWithEnum}}} {{name}}Item) {
+    {{^required}}
+    if (this.{{name}} == null) {
+      this.{{name}} = {{{defaultValue}}};
+    }
+    {{/required}}
     this.{{name}}.put(key, {{name}}Item);
     return this;
   }
diff --git a/modules/swagger-codegen/src/main/resources/JavaSpring/pojo.mustache b/modules/swagger-codegen/src/main/resources/JavaSpring/pojo.mustache
index 90aa94b923..73464e2599 100644
--- a/modules/swagger-codegen/src/main/resources/JavaSpring/pojo.mustache
+++ b/modules/swagger-codegen/src/main/resources/JavaSpring/pojo.mustache
@@ -43,6 +43,11 @@ public class {{classname}} {{#parent}}extends {{{parent}}}{{/parent}} {{#seriali
   {{#isListContainer}}
 
   public {{classname}} add{{nameInCamelCase}}Item({{{items.datatypeWithEnum}}} {{name}}Item) {
+    {{^required}}
+    if (this.{{name}} == null) {
+      this.{{name}} = {{{defaultValue}}};
+    }
+    {{/required}}
     this.{{name}}.add({{name}}Item);
     return this;
   }
@@ -50,6 +55,11 @@ public class {{classname}} {{#parent}}extends {{{parent}}}{{/parent}} {{#seriali
   {{#isMapContainer}}
 
   public {{classname}} put{{nameInCamelCase}}Item(String key, {{{items.datatypeWithEnum}}} {{name}}Item) {
+    {{^required}}
+    if (this.{{name}} == null) {
+      this.{{name}} = {{{defaultValue}}};
+    }
+    {{/required}}
     this.{{name}}.put(key, {{name}}Item);
     return this;
   }
diff --git a/modules/swagger-codegen/src/main/resources/MSF4J/pojo.mustache b/modules/swagger-codegen/src/main/resources/MSF4J/pojo.mustache
index eb1be44652..9a5582c8db 100644
--- a/modules/swagger-codegen/src/main/resources/MSF4J/pojo.mustache
+++ b/modules/swagger-codegen/src/main/resources/MSF4J/pojo.mustache
@@ -40,6 +40,11 @@ public class {{classname}} {{#parent}}extends {{{parent}}}{{/parent}} {{#seriali
   {{#isListContainer}}
 
   public {{classname}} add{{nameInCamelCase}}Item({{{items.datatypeWithEnum}}} {{name}}Item) {
+    {{^required}}
+    if (this.{{name}} == null) {
+      this.{{name}} = {{{defaultValue}}};
+    }
+    {{/required}}
     this.{{name}}.add({{name}}Item);
     return this;
   }
@@ -47,6 +52,11 @@ public class {{classname}} {{#parent}}extends {{{parent}}}{{/parent}} {{#seriali
   {{#isMapContainer}}
 
   public {{classname}} put{{nameInCamelCase}}Item(String key, {{{items.datatypeWithEnum}}} {{name}}Item) {
+    {{^required}}
+    if (this.{{name}} == null) {
+      this.{{name}} = {{{defaultValue}}};
+    }
+    {{/required}}
     this.{{name}}.put(key, {{name}}Item);
     return this;
   }
diff --git a/samples/client/petstore/java/feign/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java b/samples/client/petstore/java/feign/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java
index 273ff66a90..d35dfb34b9 100644
--- a/samples/client/petstore/java/feign/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java
+++ b/samples/client/petstore/java/feign/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java
@@ -39,6 +39,9 @@ public class AdditionalPropertiesClass {
   }
 
   public AdditionalPropertiesClass putMapPropertyItem(String key, String mapPropertyItem) {
+    if (this.mapProperty == null) {
+      this.mapProperty = new HashMap<String, String>();
+    }
     this.mapProperty.put(key, mapPropertyItem);
     return this;
   }
@@ -62,6 +65,9 @@ public class AdditionalPropertiesClass {
   }
 
   public AdditionalPropertiesClass putMapOfMapPropertyItem(String key, Map<String, String> mapOfMapPropertyItem) {
+    if (this.mapOfMapProperty == null) {
+      this.mapOfMapProperty = new HashMap<String, Map<String, String>>();
+    }
     this.mapOfMapProperty.put(key, mapOfMapPropertyItem);
     return this;
   }
diff --git a/samples/client/petstore/java/feign/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java b/samples/client/petstore/java/feign/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java
index c5eeb66b5a..01c8634bf4 100644
--- a/samples/client/petstore/java/feign/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/feign/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java
@@ -36,6 +36,9 @@ public class ArrayOfArrayOfNumberOnly {
   }
 
   public ArrayOfArrayOfNumberOnly addArrayArrayNumberItem(List<BigDecimal> arrayArrayNumberItem) {
+    if (this.arrayArrayNumber == null) {
+      this.arrayArrayNumber = new ArrayList<List<BigDecimal>>();
+    }
     this.arrayArrayNumber.add(arrayArrayNumberItem);
     return this;
   }
diff --git a/samples/client/petstore/java/feign/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java b/samples/client/petstore/java/feign/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java
index 6b749b0bec..a5ce7de4b6 100644
--- a/samples/client/petstore/java/feign/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/feign/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java
@@ -36,6 +36,9 @@ public class ArrayOfNumberOnly {
   }
 
   public ArrayOfNumberOnly addArrayNumberItem(BigDecimal arrayNumberItem) {
+    if (this.arrayNumber == null) {
+      this.arrayNumber = new ArrayList<BigDecimal>();
+    }
     this.arrayNumber.add(arrayNumberItem);
     return this;
   }
diff --git a/samples/client/petstore/java/feign/src/main/java/io/swagger/client/model/ArrayTest.java b/samples/client/petstore/java/feign/src/main/java/io/swagger/client/model/ArrayTest.java
index a92f45a96b..5ddd9d6bd4 100644
--- a/samples/client/petstore/java/feign/src/main/java/io/swagger/client/model/ArrayTest.java
+++ b/samples/client/petstore/java/feign/src/main/java/io/swagger/client/model/ArrayTest.java
@@ -42,6 +42,9 @@ public class ArrayTest {
   }
 
   public ArrayTest addArrayOfStringItem(String arrayOfStringItem) {
+    if (this.arrayOfString == null) {
+      this.arrayOfString = new ArrayList<String>();
+    }
     this.arrayOfString.add(arrayOfStringItem);
     return this;
   }
@@ -65,6 +68,9 @@ public class ArrayTest {
   }
 
   public ArrayTest addArrayArrayOfIntegerItem(List<Long> arrayArrayOfIntegerItem) {
+    if (this.arrayArrayOfInteger == null) {
+      this.arrayArrayOfInteger = new ArrayList<List<Long>>();
+    }
     this.arrayArrayOfInteger.add(arrayArrayOfIntegerItem);
     return this;
   }
@@ -88,6 +94,9 @@ public class ArrayTest {
   }
 
   public ArrayTest addArrayArrayOfModelItem(List<ReadOnlyFirst> arrayArrayOfModelItem) {
+    if (this.arrayArrayOfModel == null) {
+      this.arrayArrayOfModel = new ArrayList<List<ReadOnlyFirst>>();
+    }
     this.arrayArrayOfModel.add(arrayArrayOfModelItem);
     return this;
   }
diff --git a/samples/client/petstore/java/feign/src/main/java/io/swagger/client/model/EnumArrays.java b/samples/client/petstore/java/feign/src/main/java/io/swagger/client/model/EnumArrays.java
index dcbb54cd3f..1adf453102 100644
--- a/samples/client/petstore/java/feign/src/main/java/io/swagger/client/model/EnumArrays.java
+++ b/samples/client/petstore/java/feign/src/main/java/io/swagger/client/model/EnumArrays.java
@@ -116,6 +116,9 @@ public class EnumArrays {
   }
 
   public EnumArrays addArrayEnumItem(ArrayEnumEnum arrayEnumItem) {
+    if (this.arrayEnum == null) {
+      this.arrayEnum = new ArrayList<ArrayEnumEnum>();
+    }
     this.arrayEnum.add(arrayEnumItem);
     return this;
   }
diff --git a/samples/client/petstore/java/feign/src/main/java/io/swagger/client/model/MapTest.java b/samples/client/petstore/java/feign/src/main/java/io/swagger/client/model/MapTest.java
index 92b0d6e5b5..5243110820 100644
--- a/samples/client/petstore/java/feign/src/main/java/io/swagger/client/model/MapTest.java
+++ b/samples/client/petstore/java/feign/src/main/java/io/swagger/client/model/MapTest.java
@@ -69,6 +69,9 @@ public class MapTest {
   }
 
   public MapTest putMapMapOfStringItem(String key, Map<String, String> mapMapOfStringItem) {
+    if (this.mapMapOfString == null) {
+      this.mapMapOfString = new HashMap<String, Map<String, String>>();
+    }
     this.mapMapOfString.put(key, mapMapOfStringItem);
     return this;
   }
@@ -92,6 +95,9 @@ public class MapTest {
   }
 
   public MapTest putMapOfEnumStringItem(String key, InnerEnum mapOfEnumStringItem) {
+    if (this.mapOfEnumString == null) {
+      this.mapOfEnumString = new HashMap<String, InnerEnum>();
+    }
     this.mapOfEnumString.put(key, mapOfEnumStringItem);
     return this;
   }
diff --git a/samples/client/petstore/java/feign/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java b/samples/client/petstore/java/feign/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java
index ab7270ac76..05749b4f3d 100644
--- a/samples/client/petstore/java/feign/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java
+++ b/samples/client/petstore/java/feign/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java
@@ -81,6 +81,9 @@ public class MixedPropertiesAndAdditionalPropertiesClass {
   }
 
   public MixedPropertiesAndAdditionalPropertiesClass putMapItem(String key, Animal mapItem) {
+    if (this.map == null) {
+      this.map = new HashMap<String, Animal>();
+    }
     this.map.put(key, mapItem);
     return this;
   }
diff --git a/samples/client/petstore/java/feign/src/main/java/io/swagger/client/model/Pet.java b/samples/client/petstore/java/feign/src/main/java/io/swagger/client/model/Pet.java
index ac99ff6663..c99528a28c 100644
--- a/samples/client/petstore/java/feign/src/main/java/io/swagger/client/model/Pet.java
+++ b/samples/client/petstore/java/feign/src/main/java/io/swagger/client/model/Pet.java
@@ -161,6 +161,9 @@ public class Pet {
   }
 
   public Pet addTagsItem(Tag tagsItem) {
+    if (this.tags == null) {
+      this.tags = new ArrayList<Tag>();
+    }
     this.tags.add(tagsItem);
     return this;
   }
diff --git a/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java b/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java
index 273ff66a90..d35dfb34b9 100644
--- a/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java
+++ b/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java
@@ -39,6 +39,9 @@ public class AdditionalPropertiesClass {
   }
 
   public AdditionalPropertiesClass putMapPropertyItem(String key, String mapPropertyItem) {
+    if (this.mapProperty == null) {
+      this.mapProperty = new HashMap<String, String>();
+    }
     this.mapProperty.put(key, mapPropertyItem);
     return this;
   }
@@ -62,6 +65,9 @@ public class AdditionalPropertiesClass {
   }
 
   public AdditionalPropertiesClass putMapOfMapPropertyItem(String key, Map<String, String> mapOfMapPropertyItem) {
+    if (this.mapOfMapProperty == null) {
+      this.mapOfMapProperty = new HashMap<String, Map<String, String>>();
+    }
     this.mapOfMapProperty.put(key, mapOfMapPropertyItem);
     return this;
   }
diff --git a/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java b/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java
index c5eeb66b5a..01c8634bf4 100644
--- a/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java
@@ -36,6 +36,9 @@ public class ArrayOfArrayOfNumberOnly {
   }
 
   public ArrayOfArrayOfNumberOnly addArrayArrayNumberItem(List<BigDecimal> arrayArrayNumberItem) {
+    if (this.arrayArrayNumber == null) {
+      this.arrayArrayNumber = new ArrayList<List<BigDecimal>>();
+    }
     this.arrayArrayNumber.add(arrayArrayNumberItem);
     return this;
   }
diff --git a/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java b/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java
index 6b749b0bec..a5ce7de4b6 100644
--- a/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java
@@ -36,6 +36,9 @@ public class ArrayOfNumberOnly {
   }
 
   public ArrayOfNumberOnly addArrayNumberItem(BigDecimal arrayNumberItem) {
+    if (this.arrayNumber == null) {
+      this.arrayNumber = new ArrayList<BigDecimal>();
+    }
     this.arrayNumber.add(arrayNumberItem);
     return this;
   }
diff --git a/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/model/ArrayTest.java b/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/model/ArrayTest.java
index a92f45a96b..5ddd9d6bd4 100644
--- a/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/model/ArrayTest.java
+++ b/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/model/ArrayTest.java
@@ -42,6 +42,9 @@ public class ArrayTest {
   }
 
   public ArrayTest addArrayOfStringItem(String arrayOfStringItem) {
+    if (this.arrayOfString == null) {
+      this.arrayOfString = new ArrayList<String>();
+    }
     this.arrayOfString.add(arrayOfStringItem);
     return this;
   }
@@ -65,6 +68,9 @@ public class ArrayTest {
   }
 
   public ArrayTest addArrayArrayOfIntegerItem(List<Long> arrayArrayOfIntegerItem) {
+    if (this.arrayArrayOfInteger == null) {
+      this.arrayArrayOfInteger = new ArrayList<List<Long>>();
+    }
     this.arrayArrayOfInteger.add(arrayArrayOfIntegerItem);
     return this;
   }
@@ -88,6 +94,9 @@ public class ArrayTest {
   }
 
   public ArrayTest addArrayArrayOfModelItem(List<ReadOnlyFirst> arrayArrayOfModelItem) {
+    if (this.arrayArrayOfModel == null) {
+      this.arrayArrayOfModel = new ArrayList<List<ReadOnlyFirst>>();
+    }
     this.arrayArrayOfModel.add(arrayArrayOfModelItem);
     return this;
   }
diff --git a/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/model/EnumArrays.java b/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/model/EnumArrays.java
index dcbb54cd3f..1adf453102 100644
--- a/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/model/EnumArrays.java
+++ b/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/model/EnumArrays.java
@@ -116,6 +116,9 @@ public class EnumArrays {
   }
 
   public EnumArrays addArrayEnumItem(ArrayEnumEnum arrayEnumItem) {
+    if (this.arrayEnum == null) {
+      this.arrayEnum = new ArrayList<ArrayEnumEnum>();
+    }
     this.arrayEnum.add(arrayEnumItem);
     return this;
   }
diff --git a/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/model/MapTest.java b/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/model/MapTest.java
index 92b0d6e5b5..5243110820 100644
--- a/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/model/MapTest.java
+++ b/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/model/MapTest.java
@@ -69,6 +69,9 @@ public class MapTest {
   }
 
   public MapTest putMapMapOfStringItem(String key, Map<String, String> mapMapOfStringItem) {
+    if (this.mapMapOfString == null) {
+      this.mapMapOfString = new HashMap<String, Map<String, String>>();
+    }
     this.mapMapOfString.put(key, mapMapOfStringItem);
     return this;
   }
@@ -92,6 +95,9 @@ public class MapTest {
   }
 
   public MapTest putMapOfEnumStringItem(String key, InnerEnum mapOfEnumStringItem) {
+    if (this.mapOfEnumString == null) {
+      this.mapOfEnumString = new HashMap<String, InnerEnum>();
+    }
     this.mapOfEnumString.put(key, mapOfEnumStringItem);
     return this;
   }
diff --git a/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java b/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java
index ab7270ac76..05749b4f3d 100644
--- a/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java
+++ b/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java
@@ -81,6 +81,9 @@ public class MixedPropertiesAndAdditionalPropertiesClass {
   }
 
   public MixedPropertiesAndAdditionalPropertiesClass putMapItem(String key, Animal mapItem) {
+    if (this.map == null) {
+      this.map = new HashMap<String, Animal>();
+    }
     this.map.put(key, mapItem);
     return this;
   }
diff --git a/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/model/Pet.java b/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/model/Pet.java
index ac99ff6663..c99528a28c 100644
--- a/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/model/Pet.java
+++ b/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/model/Pet.java
@@ -161,6 +161,9 @@ public class Pet {
   }
 
   public Pet addTagsItem(Tag tagsItem) {
+    if (this.tags == null) {
+      this.tags = new ArrayList<Tag>();
+    }
     this.tags.add(tagsItem);
     return this;
   }
diff --git a/samples/client/petstore/java/jersey2-java6/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java b/samples/client/petstore/java/jersey2-java6/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java
index 2ab888265d..be2c11fff7 100644
--- a/samples/client/petstore/java/jersey2-java6/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java
+++ b/samples/client/petstore/java/jersey2-java6/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java
@@ -39,6 +39,9 @@ public class AdditionalPropertiesClass {
   }
 
   public AdditionalPropertiesClass putMapPropertyItem(String key, String mapPropertyItem) {
+    if (this.mapProperty == null) {
+      this.mapProperty = new HashMap<String, String>();
+    }
     this.mapProperty.put(key, mapPropertyItem);
     return this;
   }
@@ -62,6 +65,9 @@ public class AdditionalPropertiesClass {
   }
 
   public AdditionalPropertiesClass putMapOfMapPropertyItem(String key, Map<String, String> mapOfMapPropertyItem) {
+    if (this.mapOfMapProperty == null) {
+      this.mapOfMapProperty = new HashMap<String, Map<String, String>>();
+    }
     this.mapOfMapProperty.put(key, mapOfMapPropertyItem);
     return this;
   }
diff --git a/samples/client/petstore/java/jersey2-java6/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java b/samples/client/petstore/java/jersey2-java6/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java
index 843c806cb5..c07ad8757e 100644
--- a/samples/client/petstore/java/jersey2-java6/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/jersey2-java6/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java
@@ -36,6 +36,9 @@ public class ArrayOfArrayOfNumberOnly {
   }
 
   public ArrayOfArrayOfNumberOnly addArrayArrayNumberItem(List<BigDecimal> arrayArrayNumberItem) {
+    if (this.arrayArrayNumber == null) {
+      this.arrayArrayNumber = new ArrayList<List<BigDecimal>>();
+    }
     this.arrayArrayNumber.add(arrayArrayNumberItem);
     return this;
   }
diff --git a/samples/client/petstore/java/jersey2-java6/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java b/samples/client/petstore/java/jersey2-java6/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java
index 79395899b0..48671f1134 100644
--- a/samples/client/petstore/java/jersey2-java6/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/jersey2-java6/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java
@@ -36,6 +36,9 @@ public class ArrayOfNumberOnly {
   }
 
   public ArrayOfNumberOnly addArrayNumberItem(BigDecimal arrayNumberItem) {
+    if (this.arrayNumber == null) {
+      this.arrayNumber = new ArrayList<BigDecimal>();
+    }
     this.arrayNumber.add(arrayNumberItem);
     return this;
   }
diff --git a/samples/client/petstore/java/jersey2-java6/src/main/java/io/swagger/client/model/ArrayTest.java b/samples/client/petstore/java/jersey2-java6/src/main/java/io/swagger/client/model/ArrayTest.java
index b9f244b171..3077818d0c 100644
--- a/samples/client/petstore/java/jersey2-java6/src/main/java/io/swagger/client/model/ArrayTest.java
+++ b/samples/client/petstore/java/jersey2-java6/src/main/java/io/swagger/client/model/ArrayTest.java
@@ -42,6 +42,9 @@ public class ArrayTest {
   }
 
   public ArrayTest addArrayOfStringItem(String arrayOfStringItem) {
+    if (this.arrayOfString == null) {
+      this.arrayOfString = new ArrayList<String>();
+    }
     this.arrayOfString.add(arrayOfStringItem);
     return this;
   }
@@ -65,6 +68,9 @@ public class ArrayTest {
   }
 
   public ArrayTest addArrayArrayOfIntegerItem(List<Long> arrayArrayOfIntegerItem) {
+    if (this.arrayArrayOfInteger == null) {
+      this.arrayArrayOfInteger = new ArrayList<List<Long>>();
+    }
     this.arrayArrayOfInteger.add(arrayArrayOfIntegerItem);
     return this;
   }
@@ -88,6 +94,9 @@ public class ArrayTest {
   }
 
   public ArrayTest addArrayArrayOfModelItem(List<ReadOnlyFirst> arrayArrayOfModelItem) {
+    if (this.arrayArrayOfModel == null) {
+      this.arrayArrayOfModel = new ArrayList<List<ReadOnlyFirst>>();
+    }
     this.arrayArrayOfModel.add(arrayArrayOfModelItem);
     return this;
   }
diff --git a/samples/client/petstore/java/jersey2-java6/src/main/java/io/swagger/client/model/EnumArrays.java b/samples/client/petstore/java/jersey2-java6/src/main/java/io/swagger/client/model/EnumArrays.java
index 14e3162726..d28912b212 100644
--- a/samples/client/petstore/java/jersey2-java6/src/main/java/io/swagger/client/model/EnumArrays.java
+++ b/samples/client/petstore/java/jersey2-java6/src/main/java/io/swagger/client/model/EnumArrays.java
@@ -116,6 +116,9 @@ public class EnumArrays {
   }
 
   public EnumArrays addArrayEnumItem(ArrayEnumEnum arrayEnumItem) {
+    if (this.arrayEnum == null) {
+      this.arrayEnum = new ArrayList<ArrayEnumEnum>();
+    }
     this.arrayEnum.add(arrayEnumItem);
     return this;
   }
diff --git a/samples/client/petstore/java/jersey2-java6/src/main/java/io/swagger/client/model/MapTest.java b/samples/client/petstore/java/jersey2-java6/src/main/java/io/swagger/client/model/MapTest.java
index 290f98bfbf..cd9da863ad 100644
--- a/samples/client/petstore/java/jersey2-java6/src/main/java/io/swagger/client/model/MapTest.java
+++ b/samples/client/petstore/java/jersey2-java6/src/main/java/io/swagger/client/model/MapTest.java
@@ -69,6 +69,9 @@ public class MapTest {
   }
 
   public MapTest putMapMapOfStringItem(String key, Map<String, String> mapMapOfStringItem) {
+    if (this.mapMapOfString == null) {
+      this.mapMapOfString = new HashMap<String, Map<String, String>>();
+    }
     this.mapMapOfString.put(key, mapMapOfStringItem);
     return this;
   }
@@ -92,6 +95,9 @@ public class MapTest {
   }
 
   public MapTest putMapOfEnumStringItem(String key, InnerEnum mapOfEnumStringItem) {
+    if (this.mapOfEnumString == null) {
+      this.mapOfEnumString = new HashMap<String, InnerEnum>();
+    }
     this.mapOfEnumString.put(key, mapOfEnumStringItem);
     return this;
   }
diff --git a/samples/client/petstore/java/jersey2-java6/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java b/samples/client/petstore/java/jersey2-java6/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java
index fbd78c6a35..888178fc6a 100644
--- a/samples/client/petstore/java/jersey2-java6/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java
+++ b/samples/client/petstore/java/jersey2-java6/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java
@@ -81,6 +81,9 @@ public class MixedPropertiesAndAdditionalPropertiesClass {
   }
 
   public MixedPropertiesAndAdditionalPropertiesClass putMapItem(String key, Animal mapItem) {
+    if (this.map == null) {
+      this.map = new HashMap<String, Animal>();
+    }
     this.map.put(key, mapItem);
     return this;
   }
diff --git a/samples/client/petstore/java/jersey2-java6/src/main/java/io/swagger/client/model/Pet.java b/samples/client/petstore/java/jersey2-java6/src/main/java/io/swagger/client/model/Pet.java
index 1611a840cb..d48d60ddef 100644
--- a/samples/client/petstore/java/jersey2-java6/src/main/java/io/swagger/client/model/Pet.java
+++ b/samples/client/petstore/java/jersey2-java6/src/main/java/io/swagger/client/model/Pet.java
@@ -161,6 +161,9 @@ public class Pet {
   }
 
   public Pet addTagsItem(Tag tagsItem) {
+    if (this.tags == null) {
+      this.tags = new ArrayList<Tag>();
+    }
     this.tags.add(tagsItem);
     return this;
   }
diff --git a/samples/client/petstore/java/jersey2-java8/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java b/samples/client/petstore/java/jersey2-java8/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java
index 273ff66a90..d35dfb34b9 100644
--- a/samples/client/petstore/java/jersey2-java8/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java
+++ b/samples/client/petstore/java/jersey2-java8/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java
@@ -39,6 +39,9 @@ public class AdditionalPropertiesClass {
   }
 
   public AdditionalPropertiesClass putMapPropertyItem(String key, String mapPropertyItem) {
+    if (this.mapProperty == null) {
+      this.mapProperty = new HashMap<String, String>();
+    }
     this.mapProperty.put(key, mapPropertyItem);
     return this;
   }
@@ -62,6 +65,9 @@ public class AdditionalPropertiesClass {
   }
 
   public AdditionalPropertiesClass putMapOfMapPropertyItem(String key, Map<String, String> mapOfMapPropertyItem) {
+    if (this.mapOfMapProperty == null) {
+      this.mapOfMapProperty = new HashMap<String, Map<String, String>>();
+    }
     this.mapOfMapProperty.put(key, mapOfMapPropertyItem);
     return this;
   }
diff --git a/samples/client/petstore/java/jersey2-java8/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java b/samples/client/petstore/java/jersey2-java8/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java
index c5eeb66b5a..01c8634bf4 100644
--- a/samples/client/petstore/java/jersey2-java8/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/jersey2-java8/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java
@@ -36,6 +36,9 @@ public class ArrayOfArrayOfNumberOnly {
   }
 
   public ArrayOfArrayOfNumberOnly addArrayArrayNumberItem(List<BigDecimal> arrayArrayNumberItem) {
+    if (this.arrayArrayNumber == null) {
+      this.arrayArrayNumber = new ArrayList<List<BigDecimal>>();
+    }
     this.arrayArrayNumber.add(arrayArrayNumberItem);
     return this;
   }
diff --git a/samples/client/petstore/java/jersey2-java8/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java b/samples/client/petstore/java/jersey2-java8/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java
index 6b749b0bec..a5ce7de4b6 100644
--- a/samples/client/petstore/java/jersey2-java8/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/jersey2-java8/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java
@@ -36,6 +36,9 @@ public class ArrayOfNumberOnly {
   }
 
   public ArrayOfNumberOnly addArrayNumberItem(BigDecimal arrayNumberItem) {
+    if (this.arrayNumber == null) {
+      this.arrayNumber = new ArrayList<BigDecimal>();
+    }
     this.arrayNumber.add(arrayNumberItem);
     return this;
   }
diff --git a/samples/client/petstore/java/jersey2-java8/src/main/java/io/swagger/client/model/ArrayTest.java b/samples/client/petstore/java/jersey2-java8/src/main/java/io/swagger/client/model/ArrayTest.java
index a92f45a96b..5ddd9d6bd4 100644
--- a/samples/client/petstore/java/jersey2-java8/src/main/java/io/swagger/client/model/ArrayTest.java
+++ b/samples/client/petstore/java/jersey2-java8/src/main/java/io/swagger/client/model/ArrayTest.java
@@ -42,6 +42,9 @@ public class ArrayTest {
   }
 
   public ArrayTest addArrayOfStringItem(String arrayOfStringItem) {
+    if (this.arrayOfString == null) {
+      this.arrayOfString = new ArrayList<String>();
+    }
     this.arrayOfString.add(arrayOfStringItem);
     return this;
   }
@@ -65,6 +68,9 @@ public class ArrayTest {
   }
 
   public ArrayTest addArrayArrayOfIntegerItem(List<Long> arrayArrayOfIntegerItem) {
+    if (this.arrayArrayOfInteger == null) {
+      this.arrayArrayOfInteger = new ArrayList<List<Long>>();
+    }
     this.arrayArrayOfInteger.add(arrayArrayOfIntegerItem);
     return this;
   }
@@ -88,6 +94,9 @@ public class ArrayTest {
   }
 
   public ArrayTest addArrayArrayOfModelItem(List<ReadOnlyFirst> arrayArrayOfModelItem) {
+    if (this.arrayArrayOfModel == null) {
+      this.arrayArrayOfModel = new ArrayList<List<ReadOnlyFirst>>();
+    }
     this.arrayArrayOfModel.add(arrayArrayOfModelItem);
     return this;
   }
diff --git a/samples/client/petstore/java/jersey2-java8/src/main/java/io/swagger/client/model/EnumArrays.java b/samples/client/petstore/java/jersey2-java8/src/main/java/io/swagger/client/model/EnumArrays.java
index dcbb54cd3f..1adf453102 100644
--- a/samples/client/petstore/java/jersey2-java8/src/main/java/io/swagger/client/model/EnumArrays.java
+++ b/samples/client/petstore/java/jersey2-java8/src/main/java/io/swagger/client/model/EnumArrays.java
@@ -116,6 +116,9 @@ public class EnumArrays {
   }
 
   public EnumArrays addArrayEnumItem(ArrayEnumEnum arrayEnumItem) {
+    if (this.arrayEnum == null) {
+      this.arrayEnum = new ArrayList<ArrayEnumEnum>();
+    }
     this.arrayEnum.add(arrayEnumItem);
     return this;
   }
diff --git a/samples/client/petstore/java/jersey2-java8/src/main/java/io/swagger/client/model/MapTest.java b/samples/client/petstore/java/jersey2-java8/src/main/java/io/swagger/client/model/MapTest.java
index 92b0d6e5b5..5243110820 100644
--- a/samples/client/petstore/java/jersey2-java8/src/main/java/io/swagger/client/model/MapTest.java
+++ b/samples/client/petstore/java/jersey2-java8/src/main/java/io/swagger/client/model/MapTest.java
@@ -69,6 +69,9 @@ public class MapTest {
   }
 
   public MapTest putMapMapOfStringItem(String key, Map<String, String> mapMapOfStringItem) {
+    if (this.mapMapOfString == null) {
+      this.mapMapOfString = new HashMap<String, Map<String, String>>();
+    }
     this.mapMapOfString.put(key, mapMapOfStringItem);
     return this;
   }
@@ -92,6 +95,9 @@ public class MapTest {
   }
 
   public MapTest putMapOfEnumStringItem(String key, InnerEnum mapOfEnumStringItem) {
+    if (this.mapOfEnumString == null) {
+      this.mapOfEnumString = new HashMap<String, InnerEnum>();
+    }
     this.mapOfEnumString.put(key, mapOfEnumStringItem);
     return this;
   }
diff --git a/samples/client/petstore/java/jersey2-java8/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java b/samples/client/petstore/java/jersey2-java8/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java
index d422e60df5..c6488007e1 100644
--- a/samples/client/petstore/java/jersey2-java8/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java
+++ b/samples/client/petstore/java/jersey2-java8/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java
@@ -81,6 +81,9 @@ public class MixedPropertiesAndAdditionalPropertiesClass {
   }
 
   public MixedPropertiesAndAdditionalPropertiesClass putMapItem(String key, Animal mapItem) {
+    if (this.map == null) {
+      this.map = new HashMap<String, Animal>();
+    }
     this.map.put(key, mapItem);
     return this;
   }
diff --git a/samples/client/petstore/java/jersey2-java8/src/main/java/io/swagger/client/model/Pet.java b/samples/client/petstore/java/jersey2-java8/src/main/java/io/swagger/client/model/Pet.java
index ac99ff6663..c99528a28c 100644
--- a/samples/client/petstore/java/jersey2-java8/src/main/java/io/swagger/client/model/Pet.java
+++ b/samples/client/petstore/java/jersey2-java8/src/main/java/io/swagger/client/model/Pet.java
@@ -161,6 +161,9 @@ public class Pet {
   }
 
   public Pet addTagsItem(Tag tagsItem) {
+    if (this.tags == null) {
+      this.tags = new ArrayList<Tag>();
+    }
     this.tags.add(tagsItem);
     return this;
   }
diff --git a/samples/client/petstore/java/jersey2/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java b/samples/client/petstore/java/jersey2/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java
index 273ff66a90..d35dfb34b9 100644
--- a/samples/client/petstore/java/jersey2/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java
+++ b/samples/client/petstore/java/jersey2/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java
@@ -39,6 +39,9 @@ public class AdditionalPropertiesClass {
   }
 
   public AdditionalPropertiesClass putMapPropertyItem(String key, String mapPropertyItem) {
+    if (this.mapProperty == null) {
+      this.mapProperty = new HashMap<String, String>();
+    }
     this.mapProperty.put(key, mapPropertyItem);
     return this;
   }
@@ -62,6 +65,9 @@ public class AdditionalPropertiesClass {
   }
 
   public AdditionalPropertiesClass putMapOfMapPropertyItem(String key, Map<String, String> mapOfMapPropertyItem) {
+    if (this.mapOfMapProperty == null) {
+      this.mapOfMapProperty = new HashMap<String, Map<String, String>>();
+    }
     this.mapOfMapProperty.put(key, mapOfMapPropertyItem);
     return this;
   }
diff --git a/samples/client/petstore/java/jersey2/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java b/samples/client/petstore/java/jersey2/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java
index c5eeb66b5a..01c8634bf4 100644
--- a/samples/client/petstore/java/jersey2/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/jersey2/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java
@@ -36,6 +36,9 @@ public class ArrayOfArrayOfNumberOnly {
   }
 
   public ArrayOfArrayOfNumberOnly addArrayArrayNumberItem(List<BigDecimal> arrayArrayNumberItem) {
+    if (this.arrayArrayNumber == null) {
+      this.arrayArrayNumber = new ArrayList<List<BigDecimal>>();
+    }
     this.arrayArrayNumber.add(arrayArrayNumberItem);
     return this;
   }
diff --git a/samples/client/petstore/java/jersey2/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java b/samples/client/petstore/java/jersey2/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java
index 6b749b0bec..a5ce7de4b6 100644
--- a/samples/client/petstore/java/jersey2/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/jersey2/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java
@@ -36,6 +36,9 @@ public class ArrayOfNumberOnly {
   }
 
   public ArrayOfNumberOnly addArrayNumberItem(BigDecimal arrayNumberItem) {
+    if (this.arrayNumber == null) {
+      this.arrayNumber = new ArrayList<BigDecimal>();
+    }
     this.arrayNumber.add(arrayNumberItem);
     return this;
   }
diff --git a/samples/client/petstore/java/jersey2/src/main/java/io/swagger/client/model/ArrayTest.java b/samples/client/petstore/java/jersey2/src/main/java/io/swagger/client/model/ArrayTest.java
index a92f45a96b..5ddd9d6bd4 100644
--- a/samples/client/petstore/java/jersey2/src/main/java/io/swagger/client/model/ArrayTest.java
+++ b/samples/client/petstore/java/jersey2/src/main/java/io/swagger/client/model/ArrayTest.java
@@ -42,6 +42,9 @@ public class ArrayTest {
   }
 
   public ArrayTest addArrayOfStringItem(String arrayOfStringItem) {
+    if (this.arrayOfString == null) {
+      this.arrayOfString = new ArrayList<String>();
+    }
     this.arrayOfString.add(arrayOfStringItem);
     return this;
   }
@@ -65,6 +68,9 @@ public class ArrayTest {
   }
 
   public ArrayTest addArrayArrayOfIntegerItem(List<Long> arrayArrayOfIntegerItem) {
+    if (this.arrayArrayOfInteger == null) {
+      this.arrayArrayOfInteger = new ArrayList<List<Long>>();
+    }
     this.arrayArrayOfInteger.add(arrayArrayOfIntegerItem);
     return this;
   }
@@ -88,6 +94,9 @@ public class ArrayTest {
   }
 
   public ArrayTest addArrayArrayOfModelItem(List<ReadOnlyFirst> arrayArrayOfModelItem) {
+    if (this.arrayArrayOfModel == null) {
+      this.arrayArrayOfModel = new ArrayList<List<ReadOnlyFirst>>();
+    }
     this.arrayArrayOfModel.add(arrayArrayOfModelItem);
     return this;
   }
diff --git a/samples/client/petstore/java/jersey2/src/main/java/io/swagger/client/model/EnumArrays.java b/samples/client/petstore/java/jersey2/src/main/java/io/swagger/client/model/EnumArrays.java
index dcbb54cd3f..1adf453102 100644
--- a/samples/client/petstore/java/jersey2/src/main/java/io/swagger/client/model/EnumArrays.java
+++ b/samples/client/petstore/java/jersey2/src/main/java/io/swagger/client/model/EnumArrays.java
@@ -116,6 +116,9 @@ public class EnumArrays {
   }
 
   public EnumArrays addArrayEnumItem(ArrayEnumEnum arrayEnumItem) {
+    if (this.arrayEnum == null) {
+      this.arrayEnum = new ArrayList<ArrayEnumEnum>();
+    }
     this.arrayEnum.add(arrayEnumItem);
     return this;
   }
diff --git a/samples/client/petstore/java/jersey2/src/main/java/io/swagger/client/model/MapTest.java b/samples/client/petstore/java/jersey2/src/main/java/io/swagger/client/model/MapTest.java
index 92b0d6e5b5..5243110820 100644
--- a/samples/client/petstore/java/jersey2/src/main/java/io/swagger/client/model/MapTest.java
+++ b/samples/client/petstore/java/jersey2/src/main/java/io/swagger/client/model/MapTest.java
@@ -69,6 +69,9 @@ public class MapTest {
   }
 
   public MapTest putMapMapOfStringItem(String key, Map<String, String> mapMapOfStringItem) {
+    if (this.mapMapOfString == null) {
+      this.mapMapOfString = new HashMap<String, Map<String, String>>();
+    }
     this.mapMapOfString.put(key, mapMapOfStringItem);
     return this;
   }
@@ -92,6 +95,9 @@ public class MapTest {
   }
 
   public MapTest putMapOfEnumStringItem(String key, InnerEnum mapOfEnumStringItem) {
+    if (this.mapOfEnumString == null) {
+      this.mapOfEnumString = new HashMap<String, InnerEnum>();
+    }
     this.mapOfEnumString.put(key, mapOfEnumStringItem);
     return this;
   }
diff --git a/samples/client/petstore/java/jersey2/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java b/samples/client/petstore/java/jersey2/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java
index ab7270ac76..05749b4f3d 100644
--- a/samples/client/petstore/java/jersey2/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java
+++ b/samples/client/petstore/java/jersey2/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java
@@ -81,6 +81,9 @@ public class MixedPropertiesAndAdditionalPropertiesClass {
   }
 
   public MixedPropertiesAndAdditionalPropertiesClass putMapItem(String key, Animal mapItem) {
+    if (this.map == null) {
+      this.map = new HashMap<String, Animal>();
+    }
     this.map.put(key, mapItem);
     return this;
   }
diff --git a/samples/client/petstore/java/jersey2/src/main/java/io/swagger/client/model/Pet.java b/samples/client/petstore/java/jersey2/src/main/java/io/swagger/client/model/Pet.java
index ac99ff6663..c99528a28c 100644
--- a/samples/client/petstore/java/jersey2/src/main/java/io/swagger/client/model/Pet.java
+++ b/samples/client/petstore/java/jersey2/src/main/java/io/swagger/client/model/Pet.java
@@ -161,6 +161,9 @@ public class Pet {
   }
 
   public Pet addTagsItem(Tag tagsItem) {
+    if (this.tags == null) {
+      this.tags = new ArrayList<Tag>();
+    }
     this.tags.add(tagsItem);
     return this;
   }
diff --git a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java
index 2bd4852e8e..aacc588cc4 100644
--- a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java
+++ b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java
@@ -29,10 +29,10 @@ import android.os.Parcel;
 
 public class AdditionalPropertiesClass implements Parcelable {
   @SerializedName("map_property")
-  private Map<String, String> mapProperty = new HashMap<String, String>();
+  private Map<String, String> mapProperty = null;
 
   @SerializedName("map_of_map_property")
-  private Map<String, Map<String, String>> mapOfMapProperty = new HashMap<String, Map<String, String>>();
+  private Map<String, Map<String, String>> mapOfMapProperty = null;
 
   public AdditionalPropertiesClass mapProperty(Map<String, String> mapProperty) {
     this.mapProperty = mapProperty;
@@ -40,6 +40,9 @@ public class AdditionalPropertiesClass implements Parcelable {
   }
 
   public AdditionalPropertiesClass putMapPropertyItem(String key, String mapPropertyItem) {
+    if (this.mapProperty == null) {
+      this.mapProperty = new HashMap<String, String>();
+    }
     this.mapProperty.put(key, mapPropertyItem);
     return this;
   }
@@ -63,6 +66,9 @@ public class AdditionalPropertiesClass implements Parcelable {
   }
 
   public AdditionalPropertiesClass putMapOfMapPropertyItem(String key, Map<String, String> mapOfMapPropertyItem) {
+    if (this.mapOfMapProperty == null) {
+      this.mapOfMapProperty = new HashMap<String, Map<String, String>>();
+    }
     this.mapOfMapProperty.put(key, mapOfMapPropertyItem);
     return this;
   }
diff --git a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java
index 6c98580df1..a43774eba7 100644
--- a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java
@@ -29,7 +29,7 @@ import android.os.Parcel;
 
 public class ArrayOfArrayOfNumberOnly implements Parcelable {
   @SerializedName("ArrayArrayNumber")
-  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<List<BigDecimal>>();
+  private List<List<BigDecimal>> arrayArrayNumber = null;
 
   public ArrayOfArrayOfNumberOnly arrayArrayNumber(List<List<BigDecimal>> arrayArrayNumber) {
     this.arrayArrayNumber = arrayArrayNumber;
@@ -37,6 +37,9 @@ public class ArrayOfArrayOfNumberOnly implements Parcelable {
   }
 
   public ArrayOfArrayOfNumberOnly addArrayArrayNumberItem(List<BigDecimal> arrayArrayNumberItem) {
+    if (this.arrayArrayNumber == null) {
+      this.arrayArrayNumber = new ArrayList<List<BigDecimal>>();
+    }
     this.arrayArrayNumber.add(arrayArrayNumberItem);
     return this;
   }
diff --git a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java
index faf67248e5..fe09adb2fa 100644
--- a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java
@@ -29,7 +29,7 @@ import android.os.Parcel;
 
 public class ArrayOfNumberOnly implements Parcelable {
   @SerializedName("ArrayNumber")
-  private List<BigDecimal> arrayNumber = new ArrayList<BigDecimal>();
+  private List<BigDecimal> arrayNumber = null;
 
   public ArrayOfNumberOnly arrayNumber(List<BigDecimal> arrayNumber) {
     this.arrayNumber = arrayNumber;
@@ -37,6 +37,9 @@ public class ArrayOfNumberOnly implements Parcelable {
   }
 
   public ArrayOfNumberOnly addArrayNumberItem(BigDecimal arrayNumberItem) {
+    if (this.arrayNumber == null) {
+      this.arrayNumber = new ArrayList<BigDecimal>();
+    }
     this.arrayNumber.add(arrayNumberItem);
     return this;
   }
diff --git a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/model/ArrayTest.java b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/model/ArrayTest.java
index 3e34712b7e..9d9cfcb7ed 100644
--- a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/model/ArrayTest.java
+++ b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/model/ArrayTest.java
@@ -29,13 +29,13 @@ import android.os.Parcel;
 
 public class ArrayTest implements Parcelable {
   @SerializedName("array_of_string")
-  private List<String> arrayOfString = new ArrayList<String>();
+  private List<String> arrayOfString = null;
 
   @SerializedName("array_array_of_integer")
-  private List<List<Long>> arrayArrayOfInteger = new ArrayList<List<Long>>();
+  private List<List<Long>> arrayArrayOfInteger = null;
 
   @SerializedName("array_array_of_model")
-  private List<List<ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<List<ReadOnlyFirst>>();
+  private List<List<ReadOnlyFirst>> arrayArrayOfModel = null;
 
   public ArrayTest arrayOfString(List<String> arrayOfString) {
     this.arrayOfString = arrayOfString;
@@ -43,6 +43,9 @@ public class ArrayTest implements Parcelable {
   }
 
   public ArrayTest addArrayOfStringItem(String arrayOfStringItem) {
+    if (this.arrayOfString == null) {
+      this.arrayOfString = new ArrayList<String>();
+    }
     this.arrayOfString.add(arrayOfStringItem);
     return this;
   }
@@ -66,6 +69,9 @@ public class ArrayTest implements Parcelable {
   }
 
   public ArrayTest addArrayArrayOfIntegerItem(List<Long> arrayArrayOfIntegerItem) {
+    if (this.arrayArrayOfInteger == null) {
+      this.arrayArrayOfInteger = new ArrayList<List<Long>>();
+    }
     this.arrayArrayOfInteger.add(arrayArrayOfIntegerItem);
     return this;
   }
@@ -89,6 +95,9 @@ public class ArrayTest implements Parcelable {
   }
 
   public ArrayTest addArrayArrayOfModelItem(List<ReadOnlyFirst> arrayArrayOfModelItem) {
+    if (this.arrayArrayOfModel == null) {
+      this.arrayArrayOfModel = new ArrayList<List<ReadOnlyFirst>>();
+    }
     this.arrayArrayOfModel.add(arrayArrayOfModelItem);
     return this;
   }
diff --git a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/model/EnumArrays.java b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/model/EnumArrays.java
index 8f0ed50d7c..593272046e 100644
--- a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/model/EnumArrays.java
+++ b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/model/EnumArrays.java
@@ -75,7 +75,7 @@ public class EnumArrays implements Parcelable {
   }
 
   @SerializedName("array_enum")
-  private List<ArrayEnumEnum> arrayEnum = new ArrayList<ArrayEnumEnum>();
+  private List<ArrayEnumEnum> arrayEnum = null;
 
   public EnumArrays justSymbol(JustSymbolEnum justSymbol) {
     this.justSymbol = justSymbol;
@@ -101,6 +101,9 @@ public class EnumArrays implements Parcelable {
   }
 
   public EnumArrays addArrayEnumItem(ArrayEnumEnum arrayEnumItem) {
+    if (this.arrayEnum == null) {
+      this.arrayEnum = new ArrayList<ArrayEnumEnum>();
+    }
     this.arrayEnum.add(arrayEnumItem);
     return this;
   }
diff --git a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/model/MapTest.java b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/model/MapTest.java
index eda550e267..f224e8523d 100644
--- a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/model/MapTest.java
+++ b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/model/MapTest.java
@@ -29,7 +29,7 @@ import android.os.Parcel;
 
 public class MapTest implements Parcelable {
   @SerializedName("map_map_of_string")
-  private Map<String, Map<String, String>> mapMapOfString = new HashMap<String, Map<String, String>>();
+  private Map<String, Map<String, String>> mapMapOfString = null;
 
   /**
    * Gets or Sets inner
@@ -54,7 +54,7 @@ public class MapTest implements Parcelable {
   }
 
   @SerializedName("map_of_enum_string")
-  private Map<String, InnerEnum> mapOfEnumString = new HashMap<String, InnerEnum>();
+  private Map<String, InnerEnum> mapOfEnumString = null;
 
   public MapTest mapMapOfString(Map<String, Map<String, String>> mapMapOfString) {
     this.mapMapOfString = mapMapOfString;
@@ -62,6 +62,9 @@ public class MapTest implements Parcelable {
   }
 
   public MapTest putMapMapOfStringItem(String key, Map<String, String> mapMapOfStringItem) {
+    if (this.mapMapOfString == null) {
+      this.mapMapOfString = new HashMap<String, Map<String, String>>();
+    }
     this.mapMapOfString.put(key, mapMapOfStringItem);
     return this;
   }
@@ -85,6 +88,9 @@ public class MapTest implements Parcelable {
   }
 
   public MapTest putMapOfEnumStringItem(String key, InnerEnum mapOfEnumStringItem) {
+    if (this.mapOfEnumString == null) {
+      this.mapOfEnumString = new HashMap<String, InnerEnum>();
+    }
     this.mapOfEnumString.put(key, mapOfEnumStringItem);
     return this;
   }
diff --git a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java
index 455c022291..2dd03e0892 100644
--- a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java
+++ b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java
@@ -38,7 +38,7 @@ public class MixedPropertiesAndAdditionalPropertiesClass implements Parcelable {
   private DateTime dateTime = null;
 
   @SerializedName("map")
-  private Map<String, Animal> map = new HashMap<String, Animal>();
+  private Map<String, Animal> map = null;
 
   public MixedPropertiesAndAdditionalPropertiesClass uuid(UUID uuid) {
     this.uuid = uuid;
@@ -82,6 +82,9 @@ public class MixedPropertiesAndAdditionalPropertiesClass implements Parcelable {
   }
 
   public MixedPropertiesAndAdditionalPropertiesClass putMapItem(String key, Animal mapItem) {
+    if (this.map == null) {
+      this.map = new HashMap<String, Animal>();
+    }
     this.map.put(key, mapItem);
     return this;
   }
diff --git a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/model/Pet.java b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/model/Pet.java
index 43c61fae2b..85184e4d88 100644
--- a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/model/Pet.java
+++ b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/model/Pet.java
@@ -42,7 +42,7 @@ public class Pet implements Parcelable {
   private List<String> photoUrls = new ArrayList<String>();
 
   @SerializedName("tags")
-  private List<Tag> tags = new ArrayList<Tag>();
+  private List<Tag> tags = null;
 
   /**
    * pet status in the store
@@ -155,6 +155,9 @@ public class Pet implements Parcelable {
   }
 
   public Pet addTagsItem(Tag tagsItem) {
+    if (this.tags == null) {
+      this.tags = new ArrayList<Tag>();
+    }
     this.tags.add(tagsItem);
     return this;
   }
diff --git a/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java b/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java
index 66ee977636..3d8eb14d9b 100644
--- a/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java
+++ b/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java
@@ -38,6 +38,9 @@ public class AdditionalPropertiesClass {
   }
 
   public AdditionalPropertiesClass putMapPropertyItem(String key, String mapPropertyItem) {
+    if (this.mapProperty == null) {
+      this.mapProperty = new HashMap<String, String>();
+    }
     this.mapProperty.put(key, mapPropertyItem);
     return this;
   }
@@ -61,6 +64,9 @@ public class AdditionalPropertiesClass {
   }
 
   public AdditionalPropertiesClass putMapOfMapPropertyItem(String key, Map<String, String> mapOfMapPropertyItem) {
+    if (this.mapOfMapProperty == null) {
+      this.mapOfMapProperty = new HashMap<String, Map<String, String>>();
+    }
     this.mapOfMapProperty.put(key, mapOfMapPropertyItem);
     return this;
   }
diff --git a/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java b/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java
index 576303f730..35fb30470e 100644
--- a/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java
@@ -35,6 +35,9 @@ public class ArrayOfArrayOfNumberOnly {
   }
 
   public ArrayOfArrayOfNumberOnly addArrayArrayNumberItem(List<BigDecimal> arrayArrayNumberItem) {
+    if (this.arrayArrayNumber == null) {
+      this.arrayArrayNumber = new ArrayList<List<BigDecimal>>();
+    }
     this.arrayArrayNumber.add(arrayArrayNumberItem);
     return this;
   }
diff --git a/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java b/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java
index ca61921ce7..f89e6b2342 100644
--- a/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java
@@ -35,6 +35,9 @@ public class ArrayOfNumberOnly {
   }
 
   public ArrayOfNumberOnly addArrayNumberItem(BigDecimal arrayNumberItem) {
+    if (this.arrayNumber == null) {
+      this.arrayNumber = new ArrayList<BigDecimal>();
+    }
     this.arrayNumber.add(arrayNumberItem);
     return this;
   }
diff --git a/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/model/ArrayTest.java b/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/model/ArrayTest.java
index 4d0efb12d8..48d1a9df8c 100644
--- a/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/model/ArrayTest.java
+++ b/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/model/ArrayTest.java
@@ -41,6 +41,9 @@ public class ArrayTest {
   }
 
   public ArrayTest addArrayOfStringItem(String arrayOfStringItem) {
+    if (this.arrayOfString == null) {
+      this.arrayOfString = new ArrayList<String>();
+    }
     this.arrayOfString.add(arrayOfStringItem);
     return this;
   }
@@ -64,6 +67,9 @@ public class ArrayTest {
   }
 
   public ArrayTest addArrayArrayOfIntegerItem(List<Long> arrayArrayOfIntegerItem) {
+    if (this.arrayArrayOfInteger == null) {
+      this.arrayArrayOfInteger = new ArrayList<List<Long>>();
+    }
     this.arrayArrayOfInteger.add(arrayArrayOfIntegerItem);
     return this;
   }
@@ -87,6 +93,9 @@ public class ArrayTest {
   }
 
   public ArrayTest addArrayArrayOfModelItem(List<ReadOnlyFirst> arrayArrayOfModelItem) {
+    if (this.arrayArrayOfModel == null) {
+      this.arrayArrayOfModel = new ArrayList<List<ReadOnlyFirst>>();
+    }
     this.arrayArrayOfModel.add(arrayArrayOfModelItem);
     return this;
   }
diff --git a/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/model/EnumArrays.java b/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/model/EnumArrays.java
index ce5324046b..eab37afb32 100644
--- a/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/model/EnumArrays.java
+++ b/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/model/EnumArrays.java
@@ -99,6 +99,9 @@ public class EnumArrays {
   }
 
   public EnumArrays addArrayEnumItem(ArrayEnumEnum arrayEnumItem) {
+    if (this.arrayEnum == null) {
+      this.arrayEnum = new ArrayList<ArrayEnumEnum>();
+    }
     this.arrayEnum.add(arrayEnumItem);
     return this;
   }
diff --git a/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/model/MapTest.java b/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/model/MapTest.java
index 51d8e3c972..15e118df88 100644
--- a/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/model/MapTest.java
+++ b/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/model/MapTest.java
@@ -60,6 +60,9 @@ public class MapTest {
   }
 
   public MapTest putMapMapOfStringItem(String key, Map<String, String> mapMapOfStringItem) {
+    if (this.mapMapOfString == null) {
+      this.mapMapOfString = new HashMap<String, Map<String, String>>();
+    }
     this.mapMapOfString.put(key, mapMapOfStringItem);
     return this;
   }
@@ -83,6 +86,9 @@ public class MapTest {
   }
 
   public MapTest putMapOfEnumStringItem(String key, InnerEnum mapOfEnumStringItem) {
+    if (this.mapOfEnumString == null) {
+      this.mapOfEnumString = new HashMap<String, InnerEnum>();
+    }
     this.mapOfEnumString.put(key, mapOfEnumStringItem);
     return this;
   }
diff --git a/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java b/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java
index 4116a2f7bb..c94ff2a118 100644
--- a/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java
+++ b/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java
@@ -80,6 +80,9 @@ public class MixedPropertiesAndAdditionalPropertiesClass {
   }
 
   public MixedPropertiesAndAdditionalPropertiesClass putMapItem(String key, Animal mapItem) {
+    if (this.map == null) {
+      this.map = new HashMap<String, Animal>();
+    }
     this.map.put(key, mapItem);
     return this;
   }
diff --git a/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/model/Pet.java b/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/model/Pet.java
index 2d5d7b1275..64b70ed7c5 100644
--- a/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/model/Pet.java
+++ b/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/model/Pet.java
@@ -153,6 +153,9 @@ public class Pet {
   }
 
   public Pet addTagsItem(Tag tagsItem) {
+    if (this.tags == null) {
+      this.tags = new ArrayList<Tag>();
+    }
     this.tags.add(tagsItem);
     return this;
   }
diff --git a/samples/client/petstore/java/retrofit/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java b/samples/client/petstore/java/retrofit/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java
index 66ee977636..3d8eb14d9b 100644
--- a/samples/client/petstore/java/retrofit/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java
+++ b/samples/client/petstore/java/retrofit/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java
@@ -38,6 +38,9 @@ public class AdditionalPropertiesClass {
   }
 
   public AdditionalPropertiesClass putMapPropertyItem(String key, String mapPropertyItem) {
+    if (this.mapProperty == null) {
+      this.mapProperty = new HashMap<String, String>();
+    }
     this.mapProperty.put(key, mapPropertyItem);
     return this;
   }
@@ -61,6 +64,9 @@ public class AdditionalPropertiesClass {
   }
 
   public AdditionalPropertiesClass putMapOfMapPropertyItem(String key, Map<String, String> mapOfMapPropertyItem) {
+    if (this.mapOfMapProperty == null) {
+      this.mapOfMapProperty = new HashMap<String, Map<String, String>>();
+    }
     this.mapOfMapProperty.put(key, mapOfMapPropertyItem);
     return this;
   }
diff --git a/samples/client/petstore/java/retrofit/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java b/samples/client/petstore/java/retrofit/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java
index 576303f730..35fb30470e 100644
--- a/samples/client/petstore/java/retrofit/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/retrofit/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java
@@ -35,6 +35,9 @@ public class ArrayOfArrayOfNumberOnly {
   }
 
   public ArrayOfArrayOfNumberOnly addArrayArrayNumberItem(List<BigDecimal> arrayArrayNumberItem) {
+    if (this.arrayArrayNumber == null) {
+      this.arrayArrayNumber = new ArrayList<List<BigDecimal>>();
+    }
     this.arrayArrayNumber.add(arrayArrayNumberItem);
     return this;
   }
diff --git a/samples/client/petstore/java/retrofit/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java b/samples/client/petstore/java/retrofit/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java
index ca61921ce7..f89e6b2342 100644
--- a/samples/client/petstore/java/retrofit/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/retrofit/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java
@@ -35,6 +35,9 @@ public class ArrayOfNumberOnly {
   }
 
   public ArrayOfNumberOnly addArrayNumberItem(BigDecimal arrayNumberItem) {
+    if (this.arrayNumber == null) {
+      this.arrayNumber = new ArrayList<BigDecimal>();
+    }
     this.arrayNumber.add(arrayNumberItem);
     return this;
   }
diff --git a/samples/client/petstore/java/retrofit/src/main/java/io/swagger/client/model/ArrayTest.java b/samples/client/petstore/java/retrofit/src/main/java/io/swagger/client/model/ArrayTest.java
index 4d0efb12d8..48d1a9df8c 100644
--- a/samples/client/petstore/java/retrofit/src/main/java/io/swagger/client/model/ArrayTest.java
+++ b/samples/client/petstore/java/retrofit/src/main/java/io/swagger/client/model/ArrayTest.java
@@ -41,6 +41,9 @@ public class ArrayTest {
   }
 
   public ArrayTest addArrayOfStringItem(String arrayOfStringItem) {
+    if (this.arrayOfString == null) {
+      this.arrayOfString = new ArrayList<String>();
+    }
     this.arrayOfString.add(arrayOfStringItem);
     return this;
   }
@@ -64,6 +67,9 @@ public class ArrayTest {
   }
 
   public ArrayTest addArrayArrayOfIntegerItem(List<Long> arrayArrayOfIntegerItem) {
+    if (this.arrayArrayOfInteger == null) {
+      this.arrayArrayOfInteger = new ArrayList<List<Long>>();
+    }
     this.arrayArrayOfInteger.add(arrayArrayOfIntegerItem);
     return this;
   }
@@ -87,6 +93,9 @@ public class ArrayTest {
   }
 
   public ArrayTest addArrayArrayOfModelItem(List<ReadOnlyFirst> arrayArrayOfModelItem) {
+    if (this.arrayArrayOfModel == null) {
+      this.arrayArrayOfModel = new ArrayList<List<ReadOnlyFirst>>();
+    }
     this.arrayArrayOfModel.add(arrayArrayOfModelItem);
     return this;
   }
diff --git a/samples/client/petstore/java/retrofit/src/main/java/io/swagger/client/model/EnumArrays.java b/samples/client/petstore/java/retrofit/src/main/java/io/swagger/client/model/EnumArrays.java
index ce5324046b..eab37afb32 100644
--- a/samples/client/petstore/java/retrofit/src/main/java/io/swagger/client/model/EnumArrays.java
+++ b/samples/client/petstore/java/retrofit/src/main/java/io/swagger/client/model/EnumArrays.java
@@ -99,6 +99,9 @@ public class EnumArrays {
   }
 
   public EnumArrays addArrayEnumItem(ArrayEnumEnum arrayEnumItem) {
+    if (this.arrayEnum == null) {
+      this.arrayEnum = new ArrayList<ArrayEnumEnum>();
+    }
     this.arrayEnum.add(arrayEnumItem);
     return this;
   }
diff --git a/samples/client/petstore/java/retrofit/src/main/java/io/swagger/client/model/MapTest.java b/samples/client/petstore/java/retrofit/src/main/java/io/swagger/client/model/MapTest.java
index 51d8e3c972..15e118df88 100644
--- a/samples/client/petstore/java/retrofit/src/main/java/io/swagger/client/model/MapTest.java
+++ b/samples/client/petstore/java/retrofit/src/main/java/io/swagger/client/model/MapTest.java
@@ -60,6 +60,9 @@ public class MapTest {
   }
 
   public MapTest putMapMapOfStringItem(String key, Map<String, String> mapMapOfStringItem) {
+    if (this.mapMapOfString == null) {
+      this.mapMapOfString = new HashMap<String, Map<String, String>>();
+    }
     this.mapMapOfString.put(key, mapMapOfStringItem);
     return this;
   }
@@ -83,6 +86,9 @@ public class MapTest {
   }
 
   public MapTest putMapOfEnumStringItem(String key, InnerEnum mapOfEnumStringItem) {
+    if (this.mapOfEnumString == null) {
+      this.mapOfEnumString = new HashMap<String, InnerEnum>();
+    }
     this.mapOfEnumString.put(key, mapOfEnumStringItem);
     return this;
   }
diff --git a/samples/client/petstore/java/retrofit/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java b/samples/client/petstore/java/retrofit/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java
index 4116a2f7bb..c94ff2a118 100644
--- a/samples/client/petstore/java/retrofit/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java
+++ b/samples/client/petstore/java/retrofit/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java
@@ -80,6 +80,9 @@ public class MixedPropertiesAndAdditionalPropertiesClass {
   }
 
   public MixedPropertiesAndAdditionalPropertiesClass putMapItem(String key, Animal mapItem) {
+    if (this.map == null) {
+      this.map = new HashMap<String, Animal>();
+    }
     this.map.put(key, mapItem);
     return this;
   }
diff --git a/samples/client/petstore/java/retrofit/src/main/java/io/swagger/client/model/Pet.java b/samples/client/petstore/java/retrofit/src/main/java/io/swagger/client/model/Pet.java
index 2d5d7b1275..64b70ed7c5 100644
--- a/samples/client/petstore/java/retrofit/src/main/java/io/swagger/client/model/Pet.java
+++ b/samples/client/petstore/java/retrofit/src/main/java/io/swagger/client/model/Pet.java
@@ -153,6 +153,9 @@ public class Pet {
   }
 
   public Pet addTagsItem(Tag tagsItem) {
+    if (this.tags == null) {
+      this.tags = new ArrayList<Tag>();
+    }
     this.tags.add(tagsItem);
     return this;
   }
diff --git a/samples/client/petstore/java/retrofit2-play24/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java b/samples/client/petstore/java/retrofit2-play24/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java
index 03837fb158..cc69fde91a 100644
--- a/samples/client/petstore/java/retrofit2-play24/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java
+++ b/samples/client/petstore/java/retrofit2-play24/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java
@@ -40,6 +40,9 @@ public class AdditionalPropertiesClass {
   }
 
   public AdditionalPropertiesClass putMapPropertyItem(String key, String mapPropertyItem) {
+    if (this.mapProperty == null) {
+      this.mapProperty = new HashMap<String, String>();
+    }
     this.mapProperty.put(key, mapPropertyItem);
     return this;
   }
@@ -63,6 +66,9 @@ public class AdditionalPropertiesClass {
   }
 
   public AdditionalPropertiesClass putMapOfMapPropertyItem(String key, Map<String, String> mapOfMapPropertyItem) {
+    if (this.mapOfMapProperty == null) {
+      this.mapOfMapProperty = new HashMap<String, Map<String, String>>();
+    }
     this.mapOfMapProperty.put(key, mapOfMapPropertyItem);
     return this;
   }
diff --git a/samples/client/petstore/java/retrofit2-play24/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java b/samples/client/petstore/java/retrofit2-play24/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java
index cc275b3f84..fce599722f 100644
--- a/samples/client/petstore/java/retrofit2-play24/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/retrofit2-play24/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java
@@ -37,6 +37,9 @@ public class ArrayOfArrayOfNumberOnly {
   }
 
   public ArrayOfArrayOfNumberOnly addArrayArrayNumberItem(List<BigDecimal> arrayArrayNumberItem) {
+    if (this.arrayArrayNumber == null) {
+      this.arrayArrayNumber = new ArrayList<List<BigDecimal>>();
+    }
     this.arrayArrayNumber.add(arrayArrayNumberItem);
     return this;
   }
diff --git a/samples/client/petstore/java/retrofit2-play24/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java b/samples/client/petstore/java/retrofit2-play24/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java
index 7b9446e87e..53eb740332 100644
--- a/samples/client/petstore/java/retrofit2-play24/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/retrofit2-play24/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java
@@ -37,6 +37,9 @@ public class ArrayOfNumberOnly {
   }
 
   public ArrayOfNumberOnly addArrayNumberItem(BigDecimal arrayNumberItem) {
+    if (this.arrayNumber == null) {
+      this.arrayNumber = new ArrayList<BigDecimal>();
+    }
     this.arrayNumber.add(arrayNumberItem);
     return this;
   }
diff --git a/samples/client/petstore/java/retrofit2-play24/src/main/java/io/swagger/client/model/ArrayTest.java b/samples/client/petstore/java/retrofit2-play24/src/main/java/io/swagger/client/model/ArrayTest.java
index b2499011c0..0211f83a67 100644
--- a/samples/client/petstore/java/retrofit2-play24/src/main/java/io/swagger/client/model/ArrayTest.java
+++ b/samples/client/petstore/java/retrofit2-play24/src/main/java/io/swagger/client/model/ArrayTest.java
@@ -43,6 +43,9 @@ public class ArrayTest {
   }
 
   public ArrayTest addArrayOfStringItem(String arrayOfStringItem) {
+    if (this.arrayOfString == null) {
+      this.arrayOfString = new ArrayList<String>();
+    }
     this.arrayOfString.add(arrayOfStringItem);
     return this;
   }
@@ -66,6 +69,9 @@ public class ArrayTest {
   }
 
   public ArrayTest addArrayArrayOfIntegerItem(List<Long> arrayArrayOfIntegerItem) {
+    if (this.arrayArrayOfInteger == null) {
+      this.arrayArrayOfInteger = new ArrayList<List<Long>>();
+    }
     this.arrayArrayOfInteger.add(arrayArrayOfIntegerItem);
     return this;
   }
@@ -89,6 +95,9 @@ public class ArrayTest {
   }
 
   public ArrayTest addArrayArrayOfModelItem(List<ReadOnlyFirst> arrayArrayOfModelItem) {
+    if (this.arrayArrayOfModel == null) {
+      this.arrayArrayOfModel = new ArrayList<List<ReadOnlyFirst>>();
+    }
     this.arrayArrayOfModel.add(arrayArrayOfModelItem);
     return this;
   }
diff --git a/samples/client/petstore/java/retrofit2-play24/src/main/java/io/swagger/client/model/EnumArrays.java b/samples/client/petstore/java/retrofit2-play24/src/main/java/io/swagger/client/model/EnumArrays.java
index 818cb02f2f..9222aafcf3 100644
--- a/samples/client/petstore/java/retrofit2-play24/src/main/java/io/swagger/client/model/EnumArrays.java
+++ b/samples/client/petstore/java/retrofit2-play24/src/main/java/io/swagger/client/model/EnumArrays.java
@@ -117,6 +117,9 @@ public class EnumArrays {
   }
 
   public EnumArrays addArrayEnumItem(ArrayEnumEnum arrayEnumItem) {
+    if (this.arrayEnum == null) {
+      this.arrayEnum = new ArrayList<ArrayEnumEnum>();
+    }
     this.arrayEnum.add(arrayEnumItem);
     return this;
   }
diff --git a/samples/client/petstore/java/retrofit2-play24/src/main/java/io/swagger/client/model/MapTest.java b/samples/client/petstore/java/retrofit2-play24/src/main/java/io/swagger/client/model/MapTest.java
index 080b506dea..cd4cf9f2dd 100644
--- a/samples/client/petstore/java/retrofit2-play24/src/main/java/io/swagger/client/model/MapTest.java
+++ b/samples/client/petstore/java/retrofit2-play24/src/main/java/io/swagger/client/model/MapTest.java
@@ -70,6 +70,9 @@ public class MapTest {
   }
 
   public MapTest putMapMapOfStringItem(String key, Map<String, String> mapMapOfStringItem) {
+    if (this.mapMapOfString == null) {
+      this.mapMapOfString = new HashMap<String, Map<String, String>>();
+    }
     this.mapMapOfString.put(key, mapMapOfStringItem);
     return this;
   }
@@ -93,6 +96,9 @@ public class MapTest {
   }
 
   public MapTest putMapOfEnumStringItem(String key, InnerEnum mapOfEnumStringItem) {
+    if (this.mapOfEnumString == null) {
+      this.mapOfEnumString = new HashMap<String, InnerEnum>();
+    }
     this.mapOfEnumString.put(key, mapOfEnumStringItem);
     return this;
   }
diff --git a/samples/client/petstore/java/retrofit2-play24/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java b/samples/client/petstore/java/retrofit2-play24/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java
index c3a282bf93..9f442e3ab0 100644
--- a/samples/client/petstore/java/retrofit2-play24/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java
+++ b/samples/client/petstore/java/retrofit2-play24/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java
@@ -82,6 +82,9 @@ public class MixedPropertiesAndAdditionalPropertiesClass {
   }
 
   public MixedPropertiesAndAdditionalPropertiesClass putMapItem(String key, Animal mapItem) {
+    if (this.map == null) {
+      this.map = new HashMap<String, Animal>();
+    }
     this.map.put(key, mapItem);
     return this;
   }
diff --git a/samples/client/petstore/java/retrofit2-play24/src/main/java/io/swagger/client/model/Pet.java b/samples/client/petstore/java/retrofit2-play24/src/main/java/io/swagger/client/model/Pet.java
index 1e792023f9..34761af300 100644
--- a/samples/client/petstore/java/retrofit2-play24/src/main/java/io/swagger/client/model/Pet.java
+++ b/samples/client/petstore/java/retrofit2-play24/src/main/java/io/swagger/client/model/Pet.java
@@ -164,6 +164,9 @@ public class Pet {
   }
 
   public Pet addTagsItem(Tag tagsItem) {
+    if (this.tags == null) {
+      this.tags = new ArrayList<Tag>();
+    }
     this.tags.add(tagsItem);
     return this;
   }
diff --git a/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java b/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java
index 66ee977636..3d8eb14d9b 100644
--- a/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java
+++ b/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java
@@ -38,6 +38,9 @@ public class AdditionalPropertiesClass {
   }
 
   public AdditionalPropertiesClass putMapPropertyItem(String key, String mapPropertyItem) {
+    if (this.mapProperty == null) {
+      this.mapProperty = new HashMap<String, String>();
+    }
     this.mapProperty.put(key, mapPropertyItem);
     return this;
   }
@@ -61,6 +64,9 @@ public class AdditionalPropertiesClass {
   }
 
   public AdditionalPropertiesClass putMapOfMapPropertyItem(String key, Map<String, String> mapOfMapPropertyItem) {
+    if (this.mapOfMapProperty == null) {
+      this.mapOfMapProperty = new HashMap<String, Map<String, String>>();
+    }
     this.mapOfMapProperty.put(key, mapOfMapPropertyItem);
     return this;
   }
diff --git a/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java b/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java
index 576303f730..35fb30470e 100644
--- a/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java
@@ -35,6 +35,9 @@ public class ArrayOfArrayOfNumberOnly {
   }
 
   public ArrayOfArrayOfNumberOnly addArrayArrayNumberItem(List<BigDecimal> arrayArrayNumberItem) {
+    if (this.arrayArrayNumber == null) {
+      this.arrayArrayNumber = new ArrayList<List<BigDecimal>>();
+    }
     this.arrayArrayNumber.add(arrayArrayNumberItem);
     return this;
   }
diff --git a/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java b/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java
index ca61921ce7..f89e6b2342 100644
--- a/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java
@@ -35,6 +35,9 @@ public class ArrayOfNumberOnly {
   }
 
   public ArrayOfNumberOnly addArrayNumberItem(BigDecimal arrayNumberItem) {
+    if (this.arrayNumber == null) {
+      this.arrayNumber = new ArrayList<BigDecimal>();
+    }
     this.arrayNumber.add(arrayNumberItem);
     return this;
   }
diff --git a/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/model/ArrayTest.java b/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/model/ArrayTest.java
index 4d0efb12d8..48d1a9df8c 100644
--- a/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/model/ArrayTest.java
+++ b/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/model/ArrayTest.java
@@ -41,6 +41,9 @@ public class ArrayTest {
   }
 
   public ArrayTest addArrayOfStringItem(String arrayOfStringItem) {
+    if (this.arrayOfString == null) {
+      this.arrayOfString = new ArrayList<String>();
+    }
     this.arrayOfString.add(arrayOfStringItem);
     return this;
   }
@@ -64,6 +67,9 @@ public class ArrayTest {
   }
 
   public ArrayTest addArrayArrayOfIntegerItem(List<Long> arrayArrayOfIntegerItem) {
+    if (this.arrayArrayOfInteger == null) {
+      this.arrayArrayOfInteger = new ArrayList<List<Long>>();
+    }
     this.arrayArrayOfInteger.add(arrayArrayOfIntegerItem);
     return this;
   }
@@ -87,6 +93,9 @@ public class ArrayTest {
   }
 
   public ArrayTest addArrayArrayOfModelItem(List<ReadOnlyFirst> arrayArrayOfModelItem) {
+    if (this.arrayArrayOfModel == null) {
+      this.arrayArrayOfModel = new ArrayList<List<ReadOnlyFirst>>();
+    }
     this.arrayArrayOfModel.add(arrayArrayOfModelItem);
     return this;
   }
diff --git a/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/model/EnumArrays.java b/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/model/EnumArrays.java
index ce5324046b..eab37afb32 100644
--- a/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/model/EnumArrays.java
+++ b/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/model/EnumArrays.java
@@ -99,6 +99,9 @@ public class EnumArrays {
   }
 
   public EnumArrays addArrayEnumItem(ArrayEnumEnum arrayEnumItem) {
+    if (this.arrayEnum == null) {
+      this.arrayEnum = new ArrayList<ArrayEnumEnum>();
+    }
     this.arrayEnum.add(arrayEnumItem);
     return this;
   }
diff --git a/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/model/MapTest.java b/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/model/MapTest.java
index 51d8e3c972..15e118df88 100644
--- a/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/model/MapTest.java
+++ b/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/model/MapTest.java
@@ -60,6 +60,9 @@ public class MapTest {
   }
 
   public MapTest putMapMapOfStringItem(String key, Map<String, String> mapMapOfStringItem) {
+    if (this.mapMapOfString == null) {
+      this.mapMapOfString = new HashMap<String, Map<String, String>>();
+    }
     this.mapMapOfString.put(key, mapMapOfStringItem);
     return this;
   }
@@ -83,6 +86,9 @@ public class MapTest {
   }
 
   public MapTest putMapOfEnumStringItem(String key, InnerEnum mapOfEnumStringItem) {
+    if (this.mapOfEnumString == null) {
+      this.mapOfEnumString = new HashMap<String, InnerEnum>();
+    }
     this.mapOfEnumString.put(key, mapOfEnumStringItem);
     return this;
   }
diff --git a/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java b/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java
index 4116a2f7bb..c94ff2a118 100644
--- a/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java
+++ b/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java
@@ -80,6 +80,9 @@ public class MixedPropertiesAndAdditionalPropertiesClass {
   }
 
   public MixedPropertiesAndAdditionalPropertiesClass putMapItem(String key, Animal mapItem) {
+    if (this.map == null) {
+      this.map = new HashMap<String, Animal>();
+    }
     this.map.put(key, mapItem);
     return this;
   }
diff --git a/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/model/Pet.java b/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/model/Pet.java
index 2d5d7b1275..64b70ed7c5 100644
--- a/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/model/Pet.java
+++ b/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/model/Pet.java
@@ -153,6 +153,9 @@ public class Pet {
   }
 
   public Pet addTagsItem(Tag tagsItem) {
+    if (this.tags == null) {
+      this.tags = new ArrayList<Tag>();
+    }
     this.tags.add(tagsItem);
     return this;
   }
diff --git a/samples/client/petstore/java/retrofit2rx/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java b/samples/client/petstore/java/retrofit2rx/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java
index 66ee977636..3d8eb14d9b 100644
--- a/samples/client/petstore/java/retrofit2rx/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java
+++ b/samples/client/petstore/java/retrofit2rx/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java
@@ -38,6 +38,9 @@ public class AdditionalPropertiesClass {
   }
 
   public AdditionalPropertiesClass putMapPropertyItem(String key, String mapPropertyItem) {
+    if (this.mapProperty == null) {
+      this.mapProperty = new HashMap<String, String>();
+    }
     this.mapProperty.put(key, mapPropertyItem);
     return this;
   }
@@ -61,6 +64,9 @@ public class AdditionalPropertiesClass {
   }
 
   public AdditionalPropertiesClass putMapOfMapPropertyItem(String key, Map<String, String> mapOfMapPropertyItem) {
+    if (this.mapOfMapProperty == null) {
+      this.mapOfMapProperty = new HashMap<String, Map<String, String>>();
+    }
     this.mapOfMapProperty.put(key, mapOfMapPropertyItem);
     return this;
   }
diff --git a/samples/client/petstore/java/retrofit2rx/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java b/samples/client/petstore/java/retrofit2rx/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java
index 576303f730..35fb30470e 100644
--- a/samples/client/petstore/java/retrofit2rx/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/retrofit2rx/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java
@@ -35,6 +35,9 @@ public class ArrayOfArrayOfNumberOnly {
   }
 
   public ArrayOfArrayOfNumberOnly addArrayArrayNumberItem(List<BigDecimal> arrayArrayNumberItem) {
+    if (this.arrayArrayNumber == null) {
+      this.arrayArrayNumber = new ArrayList<List<BigDecimal>>();
+    }
     this.arrayArrayNumber.add(arrayArrayNumberItem);
     return this;
   }
diff --git a/samples/client/petstore/java/retrofit2rx/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java b/samples/client/petstore/java/retrofit2rx/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java
index ca61921ce7..f89e6b2342 100644
--- a/samples/client/petstore/java/retrofit2rx/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/retrofit2rx/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java
@@ -35,6 +35,9 @@ public class ArrayOfNumberOnly {
   }
 
   public ArrayOfNumberOnly addArrayNumberItem(BigDecimal arrayNumberItem) {
+    if (this.arrayNumber == null) {
+      this.arrayNumber = new ArrayList<BigDecimal>();
+    }
     this.arrayNumber.add(arrayNumberItem);
     return this;
   }
diff --git a/samples/client/petstore/java/retrofit2rx/src/main/java/io/swagger/client/model/ArrayTest.java b/samples/client/petstore/java/retrofit2rx/src/main/java/io/swagger/client/model/ArrayTest.java
index 4d0efb12d8..48d1a9df8c 100644
--- a/samples/client/petstore/java/retrofit2rx/src/main/java/io/swagger/client/model/ArrayTest.java
+++ b/samples/client/petstore/java/retrofit2rx/src/main/java/io/swagger/client/model/ArrayTest.java
@@ -41,6 +41,9 @@ public class ArrayTest {
   }
 
   public ArrayTest addArrayOfStringItem(String arrayOfStringItem) {
+    if (this.arrayOfString == null) {
+      this.arrayOfString = new ArrayList<String>();
+    }
     this.arrayOfString.add(arrayOfStringItem);
     return this;
   }
@@ -64,6 +67,9 @@ public class ArrayTest {
   }
 
   public ArrayTest addArrayArrayOfIntegerItem(List<Long> arrayArrayOfIntegerItem) {
+    if (this.arrayArrayOfInteger == null) {
+      this.arrayArrayOfInteger = new ArrayList<List<Long>>();
+    }
     this.arrayArrayOfInteger.add(arrayArrayOfIntegerItem);
     return this;
   }
@@ -87,6 +93,9 @@ public class ArrayTest {
   }
 
   public ArrayTest addArrayArrayOfModelItem(List<ReadOnlyFirst> arrayArrayOfModelItem) {
+    if (this.arrayArrayOfModel == null) {
+      this.arrayArrayOfModel = new ArrayList<List<ReadOnlyFirst>>();
+    }
     this.arrayArrayOfModel.add(arrayArrayOfModelItem);
     return this;
   }
diff --git a/samples/client/petstore/java/retrofit2rx/src/main/java/io/swagger/client/model/EnumArrays.java b/samples/client/petstore/java/retrofit2rx/src/main/java/io/swagger/client/model/EnumArrays.java
index ce5324046b..eab37afb32 100644
--- a/samples/client/petstore/java/retrofit2rx/src/main/java/io/swagger/client/model/EnumArrays.java
+++ b/samples/client/petstore/java/retrofit2rx/src/main/java/io/swagger/client/model/EnumArrays.java
@@ -99,6 +99,9 @@ public class EnumArrays {
   }
 
   public EnumArrays addArrayEnumItem(ArrayEnumEnum arrayEnumItem) {
+    if (this.arrayEnum == null) {
+      this.arrayEnum = new ArrayList<ArrayEnumEnum>();
+    }
     this.arrayEnum.add(arrayEnumItem);
     return this;
   }
diff --git a/samples/client/petstore/java/retrofit2rx/src/main/java/io/swagger/client/model/MapTest.java b/samples/client/petstore/java/retrofit2rx/src/main/java/io/swagger/client/model/MapTest.java
index 51d8e3c972..15e118df88 100644
--- a/samples/client/petstore/java/retrofit2rx/src/main/java/io/swagger/client/model/MapTest.java
+++ b/samples/client/petstore/java/retrofit2rx/src/main/java/io/swagger/client/model/MapTest.java
@@ -60,6 +60,9 @@ public class MapTest {
   }
 
   public MapTest putMapMapOfStringItem(String key, Map<String, String> mapMapOfStringItem) {
+    if (this.mapMapOfString == null) {
+      this.mapMapOfString = new HashMap<String, Map<String, String>>();
+    }
     this.mapMapOfString.put(key, mapMapOfStringItem);
     return this;
   }
@@ -83,6 +86,9 @@ public class MapTest {
   }
 
   public MapTest putMapOfEnumStringItem(String key, InnerEnum mapOfEnumStringItem) {
+    if (this.mapOfEnumString == null) {
+      this.mapOfEnumString = new HashMap<String, InnerEnum>();
+    }
     this.mapOfEnumString.put(key, mapOfEnumStringItem);
     return this;
   }
diff --git a/samples/client/petstore/java/retrofit2rx/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java b/samples/client/petstore/java/retrofit2rx/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java
index 4116a2f7bb..c94ff2a118 100644
--- a/samples/client/petstore/java/retrofit2rx/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java
+++ b/samples/client/petstore/java/retrofit2rx/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java
@@ -80,6 +80,9 @@ public class MixedPropertiesAndAdditionalPropertiesClass {
   }
 
   public MixedPropertiesAndAdditionalPropertiesClass putMapItem(String key, Animal mapItem) {
+    if (this.map == null) {
+      this.map = new HashMap<String, Animal>();
+    }
     this.map.put(key, mapItem);
     return this;
   }
diff --git a/samples/client/petstore/java/retrofit2rx/src/main/java/io/swagger/client/model/Pet.java b/samples/client/petstore/java/retrofit2rx/src/main/java/io/swagger/client/model/Pet.java
index 2d5d7b1275..64b70ed7c5 100644
--- a/samples/client/petstore/java/retrofit2rx/src/main/java/io/swagger/client/model/Pet.java
+++ b/samples/client/petstore/java/retrofit2rx/src/main/java/io/swagger/client/model/Pet.java
@@ -153,6 +153,9 @@ public class Pet {
   }
 
   public Pet addTagsItem(Tag tagsItem) {
+    if (this.tags == null) {
+      this.tags = new ArrayList<Tag>();
+    }
     this.tags.add(tagsItem);
     return this;
   }
diff --git a/samples/client/petstore/java/retrofit2rx2/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java b/samples/client/petstore/java/retrofit2rx2/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java
index 7643088bc1..3d8eb14d9b 100644
--- a/samples/client/petstore/java/retrofit2rx2/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java
+++ b/samples/client/petstore/java/retrofit2rx2/src/main/java/io/swagger/client/model/AdditionalPropertiesClass.java
@@ -27,10 +27,10 @@ import java.util.Map;
 
 public class AdditionalPropertiesClass {
   @SerializedName("map_property")
-  private Map<String, String> mapProperty = new HashMap<String, String>();
+  private Map<String, String> mapProperty = null;
 
   @SerializedName("map_of_map_property")
-  private Map<String, Map<String, String>> mapOfMapProperty = new HashMap<String, Map<String, String>>();
+  private Map<String, Map<String, String>> mapOfMapProperty = null;
 
   public AdditionalPropertiesClass mapProperty(Map<String, String> mapProperty) {
     this.mapProperty = mapProperty;
@@ -38,6 +38,9 @@ public class AdditionalPropertiesClass {
   }
 
   public AdditionalPropertiesClass putMapPropertyItem(String key, String mapPropertyItem) {
+    if (this.mapProperty == null) {
+      this.mapProperty = new HashMap<String, String>();
+    }
     this.mapProperty.put(key, mapPropertyItem);
     return this;
   }
@@ -61,6 +64,9 @@ public class AdditionalPropertiesClass {
   }
 
   public AdditionalPropertiesClass putMapOfMapPropertyItem(String key, Map<String, String> mapOfMapPropertyItem) {
+    if (this.mapOfMapProperty == null) {
+      this.mapOfMapProperty = new HashMap<String, Map<String, String>>();
+    }
     this.mapOfMapProperty.put(key, mapOfMapPropertyItem);
     return this;
   }
diff --git a/samples/client/petstore/java/retrofit2rx2/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java b/samples/client/petstore/java/retrofit2rx2/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java
index fbc5eef2f7..35fb30470e 100644
--- a/samples/client/petstore/java/retrofit2rx2/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/retrofit2rx2/src/main/java/io/swagger/client/model/ArrayOfArrayOfNumberOnly.java
@@ -27,7 +27,7 @@ import java.util.List;
 
 public class ArrayOfArrayOfNumberOnly {
   @SerializedName("ArrayArrayNumber")
-  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<List<BigDecimal>>();
+  private List<List<BigDecimal>> arrayArrayNumber = null;
 
   public ArrayOfArrayOfNumberOnly arrayArrayNumber(List<List<BigDecimal>> arrayArrayNumber) {
     this.arrayArrayNumber = arrayArrayNumber;
@@ -35,6 +35,9 @@ public class ArrayOfArrayOfNumberOnly {
   }
 
   public ArrayOfArrayOfNumberOnly addArrayArrayNumberItem(List<BigDecimal> arrayArrayNumberItem) {
+    if (this.arrayArrayNumber == null) {
+      this.arrayArrayNumber = new ArrayList<List<BigDecimal>>();
+    }
     this.arrayArrayNumber.add(arrayArrayNumberItem);
     return this;
   }
diff --git a/samples/client/petstore/java/retrofit2rx2/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java b/samples/client/petstore/java/retrofit2rx2/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java
index 47e816f633..f89e6b2342 100644
--- a/samples/client/petstore/java/retrofit2rx2/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java
+++ b/samples/client/petstore/java/retrofit2rx2/src/main/java/io/swagger/client/model/ArrayOfNumberOnly.java
@@ -27,7 +27,7 @@ import java.util.List;
 
 public class ArrayOfNumberOnly {
   @SerializedName("ArrayNumber")
-  private List<BigDecimal> arrayNumber = new ArrayList<BigDecimal>();
+  private List<BigDecimal> arrayNumber = null;
 
   public ArrayOfNumberOnly arrayNumber(List<BigDecimal> arrayNumber) {
     this.arrayNumber = arrayNumber;
@@ -35,6 +35,9 @@ public class ArrayOfNumberOnly {
   }
 
   public ArrayOfNumberOnly addArrayNumberItem(BigDecimal arrayNumberItem) {
+    if (this.arrayNumber == null) {
+      this.arrayNumber = new ArrayList<BigDecimal>();
+    }
     this.arrayNumber.add(arrayNumberItem);
     return this;
   }
diff --git a/samples/client/petstore/java/retrofit2rx2/src/main/java/io/swagger/client/model/ArrayTest.java b/samples/client/petstore/java/retrofit2rx2/src/main/java/io/swagger/client/model/ArrayTest.java
index 39008027e2..48d1a9df8c 100644
--- a/samples/client/petstore/java/retrofit2rx2/src/main/java/io/swagger/client/model/ArrayTest.java
+++ b/samples/client/petstore/java/retrofit2rx2/src/main/java/io/swagger/client/model/ArrayTest.java
@@ -27,13 +27,13 @@ import java.util.List;
 
 public class ArrayTest {
   @SerializedName("array_of_string")
-  private List<String> arrayOfString = new ArrayList<String>();
+  private List<String> arrayOfString = null;
 
   @SerializedName("array_array_of_integer")
-  private List<List<Long>> arrayArrayOfInteger = new ArrayList<List<Long>>();
+  private List<List<Long>> arrayArrayOfInteger = null;
 
   @SerializedName("array_array_of_model")
-  private List<List<ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<List<ReadOnlyFirst>>();
+  private List<List<ReadOnlyFirst>> arrayArrayOfModel = null;
 
   public ArrayTest arrayOfString(List<String> arrayOfString) {
     this.arrayOfString = arrayOfString;
@@ -41,6 +41,9 @@ public class ArrayTest {
   }
 
   public ArrayTest addArrayOfStringItem(String arrayOfStringItem) {
+    if (this.arrayOfString == null) {
+      this.arrayOfString = new ArrayList<String>();
+    }
     this.arrayOfString.add(arrayOfStringItem);
     return this;
   }
@@ -64,6 +67,9 @@ public class ArrayTest {
   }
 
   public ArrayTest addArrayArrayOfIntegerItem(List<Long> arrayArrayOfIntegerItem) {
+    if (this.arrayArrayOfInteger == null) {
+      this.arrayArrayOfInteger = new ArrayList<List<Long>>();
+    }
     this.arrayArrayOfInteger.add(arrayArrayOfIntegerItem);
     return this;
   }
@@ -87,6 +93,9 @@ public class ArrayTest {
   }
 
   public ArrayTest addArrayArrayOfModelItem(List<ReadOnlyFirst> arrayArrayOfModelItem) {
+    if (this.arrayArrayOfModel == null) {
+      this.arrayArrayOfModel = new ArrayList<List<ReadOnlyFirst>>();
+    }
     this.arrayArrayOfModel.add(arrayArrayOfModelItem);
     return this;
   }
diff --git a/samples/client/petstore/java/retrofit2rx2/src/main/java/io/swagger/client/model/EnumArrays.java b/samples/client/petstore/java/retrofit2rx2/src/main/java/io/swagger/client/model/EnumArrays.java
index 68e8f21eb2..eab37afb32 100644
--- a/samples/client/petstore/java/retrofit2rx2/src/main/java/io/swagger/client/model/EnumArrays.java
+++ b/samples/client/petstore/java/retrofit2rx2/src/main/java/io/swagger/client/model/EnumArrays.java
@@ -73,7 +73,7 @@ public class EnumArrays {
   }
 
   @SerializedName("array_enum")
-  private List<ArrayEnumEnum> arrayEnum = new ArrayList<ArrayEnumEnum>();
+  private List<ArrayEnumEnum> arrayEnum = null;
 
   public EnumArrays justSymbol(JustSymbolEnum justSymbol) {
     this.justSymbol = justSymbol;
@@ -99,6 +99,9 @@ public class EnumArrays {
   }
 
   public EnumArrays addArrayEnumItem(ArrayEnumEnum arrayEnumItem) {
+    if (this.arrayEnum == null) {
+      this.arrayEnum = new ArrayList<ArrayEnumEnum>();
+    }
     this.arrayEnum.add(arrayEnumItem);
     return this;
   }
diff --git a/samples/client/petstore/java/retrofit2rx2/src/main/java/io/swagger/client/model/MapTest.java b/samples/client/petstore/java/retrofit2rx2/src/main/java/io/swagger/client/model/MapTest.java
index a03d25c6d1..15e118df88 100644
--- a/samples/client/petstore/java/retrofit2rx2/src/main/java/io/swagger/client/model/MapTest.java
+++ b/samples/client/petstore/java/retrofit2rx2/src/main/java/io/swagger/client/model/MapTest.java
@@ -27,7 +27,7 @@ import java.util.Map;
 
 public class MapTest {
   @SerializedName("map_map_of_string")
-  private Map<String, Map<String, String>> mapMapOfString = new HashMap<String, Map<String, String>>();
+  private Map<String, Map<String, String>> mapMapOfString = null;
 
   /**
    * Gets or Sets inner
@@ -52,7 +52,7 @@ public class MapTest {
   }
 
   @SerializedName("map_of_enum_string")
-  private Map<String, InnerEnum> mapOfEnumString = new HashMap<String, InnerEnum>();
+  private Map<String, InnerEnum> mapOfEnumString = null;
 
   public MapTest mapMapOfString(Map<String, Map<String, String>> mapMapOfString) {
     this.mapMapOfString = mapMapOfString;
@@ -60,6 +60,9 @@ public class MapTest {
   }
 
   public MapTest putMapMapOfStringItem(String key, Map<String, String> mapMapOfStringItem) {
+    if (this.mapMapOfString == null) {
+      this.mapMapOfString = new HashMap<String, Map<String, String>>();
+    }
     this.mapMapOfString.put(key, mapMapOfStringItem);
     return this;
   }
@@ -83,6 +86,9 @@ public class MapTest {
   }
 
   public MapTest putMapOfEnumStringItem(String key, InnerEnum mapOfEnumStringItem) {
+    if (this.mapOfEnumString == null) {
+      this.mapOfEnumString = new HashMap<String, InnerEnum>();
+    }
     this.mapOfEnumString.put(key, mapOfEnumStringItem);
     return this;
   }
diff --git a/samples/client/petstore/java/retrofit2rx2/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java b/samples/client/petstore/java/retrofit2rx2/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java
index 13487e7e35..c94ff2a118 100644
--- a/samples/client/petstore/java/retrofit2rx2/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java
+++ b/samples/client/petstore/java/retrofit2rx2/src/main/java/io/swagger/client/model/MixedPropertiesAndAdditionalPropertiesClass.java
@@ -36,7 +36,7 @@ public class MixedPropertiesAndAdditionalPropertiesClass {
   private DateTime dateTime = null;
 
   @SerializedName("map")
-  private Map<String, Animal> map = new HashMap<String, Animal>();
+  private Map<String, Animal> map = null;
 
   public MixedPropertiesAndAdditionalPropertiesClass uuid(UUID uuid) {
     this.uuid = uuid;
@@ -80,6 +80,9 @@ public class MixedPropertiesAndAdditionalPropertiesClass {
   }
 
   public MixedPropertiesAndAdditionalPropertiesClass putMapItem(String key, Animal mapItem) {
+    if (this.map == null) {
+      this.map = new HashMap<String, Animal>();
+    }
     this.map.put(key, mapItem);
     return this;
   }
diff --git a/samples/client/petstore/java/retrofit2rx2/src/main/java/io/swagger/client/model/Pet.java b/samples/client/petstore/java/retrofit2rx2/src/main/java/io/swagger/client/model/Pet.java
index 8b330f6ebb..64b70ed7c5 100644
--- a/samples/client/petstore/java/retrofit2rx2/src/main/java/io/swagger/client/model/Pet.java
+++ b/samples/client/petstore/java/retrofit2rx2/src/main/java/io/swagger/client/model/Pet.java
@@ -40,7 +40,7 @@ public class Pet {
   private List<String> photoUrls = new ArrayList<String>();
 
   @SerializedName("tags")
-  private List<Tag> tags = new ArrayList<Tag>();
+  private List<Tag> tags = null;
 
   /**
    * pet status in the store
@@ -153,6 +153,9 @@ public class Pet {
   }
 
   public Pet addTagsItem(Tag tagsItem) {
+    if (this.tags == null) {
+      this.tags = new ArrayList<Tag>();
+    }
     this.tags.add(tagsItem);
     return this;
   }
diff --git a/samples/client/petstore/spring-cloud/src/main/java/io/swagger/model/Pet.java b/samples/client/petstore/spring-cloud/src/main/java/io/swagger/model/Pet.java
index c666cf2103..159b993ed3 100644
--- a/samples/client/petstore/spring-cloud/src/main/java/io/swagger/model/Pet.java
+++ b/samples/client/petstore/spring-cloud/src/main/java/io/swagger/model/Pet.java
@@ -153,6 +153,9 @@ public class Pet   {
   }
 
   public Pet addTagsItem(Tag tagsItem) {
+    if (this.tags == null) {
+      this.tags = new ArrayList<Tag>();
+    }
     this.tags.add(tagsItem);
     return this;
   }
diff --git a/samples/client/petstore/spring-stubs/src/main/java/io/swagger/model/Pet.java b/samples/client/petstore/spring-stubs/src/main/java/io/swagger/model/Pet.java
index c666cf2103..159b993ed3 100644
--- a/samples/client/petstore/spring-stubs/src/main/java/io/swagger/model/Pet.java
+++ b/samples/client/petstore/spring-stubs/src/main/java/io/swagger/model/Pet.java
@@ -153,6 +153,9 @@ public class Pet   {
   }
 
   public Pet addTagsItem(Tag tagsItem) {
+    if (this.tags == null) {
+      this.tags = new ArrayList<Tag>();
+    }
     this.tags.add(tagsItem);
     return this;
   }
diff --git a/samples/server/petstore/java-msf4j/src/gen/java/io/swagger/model/AdditionalPropertiesClass.java b/samples/server/petstore/java-msf4j/src/gen/java/io/swagger/model/AdditionalPropertiesClass.java
index 488f1acade..789fe0cd3c 100644
--- a/samples/server/petstore/java-msf4j/src/gen/java/io/swagger/model/AdditionalPropertiesClass.java
+++ b/samples/server/petstore/java-msf4j/src/gen/java/io/swagger/model/AdditionalPropertiesClass.java
@@ -26,6 +26,9 @@ public class AdditionalPropertiesClass   {
   }
 
   public AdditionalPropertiesClass putMapPropertyItem(String key, String mapPropertyItem) {
+    if (this.mapProperty == null) {
+      this.mapProperty = new HashMap<String, String>();
+    }
     this.mapProperty.put(key, mapPropertyItem);
     return this;
   }
@@ -49,6 +52,9 @@ public class AdditionalPropertiesClass   {
   }
 
   public AdditionalPropertiesClass putMapOfMapPropertyItem(String key, Map<String, String> mapOfMapPropertyItem) {
+    if (this.mapOfMapProperty == null) {
+      this.mapOfMapProperty = new HashMap<String, Map<String, String>>();
+    }
     this.mapOfMapProperty.put(key, mapOfMapPropertyItem);
     return this;
   }
diff --git a/samples/server/petstore/java-msf4j/src/gen/java/io/swagger/model/ArrayOfArrayOfNumberOnly.java b/samples/server/petstore/java-msf4j/src/gen/java/io/swagger/model/ArrayOfArrayOfNumberOnly.java
index f914ff03eb..37112db97e 100644
--- a/samples/server/petstore/java-msf4j/src/gen/java/io/swagger/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/server/petstore/java-msf4j/src/gen/java/io/swagger/model/ArrayOfArrayOfNumberOnly.java
@@ -23,6 +23,9 @@ public class ArrayOfArrayOfNumberOnly   {
   }
 
   public ArrayOfArrayOfNumberOnly addArrayArrayNumberItem(List<BigDecimal> arrayArrayNumberItem) {
+    if (this.arrayArrayNumber == null) {
+      this.arrayArrayNumber = new ArrayList<List<BigDecimal>>();
+    }
     this.arrayArrayNumber.add(arrayArrayNumberItem);
     return this;
   }
diff --git a/samples/server/petstore/java-msf4j/src/gen/java/io/swagger/model/ArrayOfNumberOnly.java b/samples/server/petstore/java-msf4j/src/gen/java/io/swagger/model/ArrayOfNumberOnly.java
index 457d8ffc54..690c5841b5 100644
--- a/samples/server/petstore/java-msf4j/src/gen/java/io/swagger/model/ArrayOfNumberOnly.java
+++ b/samples/server/petstore/java-msf4j/src/gen/java/io/swagger/model/ArrayOfNumberOnly.java
@@ -23,6 +23,9 @@ public class ArrayOfNumberOnly   {
   }
 
   public ArrayOfNumberOnly addArrayNumberItem(BigDecimal arrayNumberItem) {
+    if (this.arrayNumber == null) {
+      this.arrayNumber = new ArrayList<BigDecimal>();
+    }
     this.arrayNumber.add(arrayNumberItem);
     return this;
   }
diff --git a/samples/server/petstore/java-msf4j/src/gen/java/io/swagger/model/ArrayTest.java b/samples/server/petstore/java-msf4j/src/gen/java/io/swagger/model/ArrayTest.java
index 4df8614f41..db67fc5a92 100644
--- a/samples/server/petstore/java-msf4j/src/gen/java/io/swagger/model/ArrayTest.java
+++ b/samples/server/petstore/java-msf4j/src/gen/java/io/swagger/model/ArrayTest.java
@@ -29,6 +29,9 @@ public class ArrayTest   {
   }
 
   public ArrayTest addArrayOfStringItem(String arrayOfStringItem) {
+    if (this.arrayOfString == null) {
+      this.arrayOfString = new ArrayList<String>();
+    }
     this.arrayOfString.add(arrayOfStringItem);
     return this;
   }
@@ -52,6 +55,9 @@ public class ArrayTest   {
   }
 
   public ArrayTest addArrayArrayOfIntegerItem(List<Long> arrayArrayOfIntegerItem) {
+    if (this.arrayArrayOfInteger == null) {
+      this.arrayArrayOfInteger = new ArrayList<List<Long>>();
+    }
     this.arrayArrayOfInteger.add(arrayArrayOfIntegerItem);
     return this;
   }
@@ -75,6 +81,9 @@ public class ArrayTest   {
   }
 
   public ArrayTest addArrayArrayOfModelItem(List<ReadOnlyFirst> arrayArrayOfModelItem) {
+    if (this.arrayArrayOfModel == null) {
+      this.arrayArrayOfModel = new ArrayList<List<ReadOnlyFirst>>();
+    }
     this.arrayArrayOfModel.add(arrayArrayOfModelItem);
     return this;
   }
diff --git a/samples/server/petstore/java-msf4j/src/gen/java/io/swagger/model/EnumArrays.java b/samples/server/petstore/java-msf4j/src/gen/java/io/swagger/model/EnumArrays.java
index 7f3efbc690..55358c076b 100644
--- a/samples/server/petstore/java-msf4j/src/gen/java/io/swagger/model/EnumArrays.java
+++ b/samples/server/petstore/java-msf4j/src/gen/java/io/swagger/model/EnumArrays.java
@@ -106,6 +106,9 @@ public class EnumArrays   {
   }
 
   public EnumArrays addArrayEnumItem(ArrayEnumEnum arrayEnumItem) {
+    if (this.arrayEnum == null) {
+      this.arrayEnum = new ArrayList<ArrayEnumEnum>();
+    }
     this.arrayEnum.add(arrayEnumItem);
     return this;
   }
diff --git a/samples/server/petstore/java-msf4j/src/gen/java/io/swagger/model/MapTest.java b/samples/server/petstore/java-msf4j/src/gen/java/io/swagger/model/MapTest.java
index 89af83736c..1ff2f59e99 100644
--- a/samples/server/petstore/java-msf4j/src/gen/java/io/swagger/model/MapTest.java
+++ b/samples/server/petstore/java-msf4j/src/gen/java/io/swagger/model/MapTest.java
@@ -58,6 +58,9 @@ public class MapTest   {
   }
 
   public MapTest putMapMapOfStringItem(String key, Map<String, String> mapMapOfStringItem) {
+    if (this.mapMapOfString == null) {
+      this.mapMapOfString = new HashMap<String, Map<String, String>>();
+    }
     this.mapMapOfString.put(key, mapMapOfStringItem);
     return this;
   }
@@ -81,6 +84,9 @@ public class MapTest   {
   }
 
   public MapTest putMapOfEnumStringItem(String key, InnerEnum mapOfEnumStringItem) {
+    if (this.mapOfEnumString == null) {
+      this.mapOfEnumString = new HashMap<String, InnerEnum>();
+    }
     this.mapOfEnumString.put(key, mapOfEnumStringItem);
     return this;
   }
diff --git a/samples/server/petstore/java-msf4j/src/gen/java/io/swagger/model/MixedPropertiesAndAdditionalPropertiesClass.java b/samples/server/petstore/java-msf4j/src/gen/java/io/swagger/model/MixedPropertiesAndAdditionalPropertiesClass.java
index fad1ab502c..b784a93830 100644
--- a/samples/server/petstore/java-msf4j/src/gen/java/io/swagger/model/MixedPropertiesAndAdditionalPropertiesClass.java
+++ b/samples/server/petstore/java-msf4j/src/gen/java/io/swagger/model/MixedPropertiesAndAdditionalPropertiesClass.java
@@ -68,6 +68,9 @@ public class MixedPropertiesAndAdditionalPropertiesClass   {
   }
 
   public MixedPropertiesAndAdditionalPropertiesClass putMapItem(String key, Animal mapItem) {
+    if (this.map == null) {
+      this.map = new HashMap<String, Animal>();
+    }
     this.map.put(key, mapItem);
     return this;
   }
diff --git a/samples/server/petstore/java-msf4j/src/gen/java/io/swagger/model/Pet.java b/samples/server/petstore/java-msf4j/src/gen/java/io/swagger/model/Pet.java
index bbaacde9ee..dbbf22e859 100644
--- a/samples/server/petstore/java-msf4j/src/gen/java/io/swagger/model/Pet.java
+++ b/samples/server/petstore/java-msf4j/src/gen/java/io/swagger/model/Pet.java
@@ -150,6 +150,9 @@ public class Pet   {
   }
 
   public Pet addTagsItem(Tag tagsItem) {
+    if (this.tags == null) {
+      this.tags = new ArrayList<Tag>();
+    }
     this.tags.add(tagsItem);
     return this;
   }
diff --git a/samples/server/petstore/java-play-framework/app/apimodels/Pet.java b/samples/server/petstore/java-play-framework/app/apimodels/Pet.java
index e274b14fa5..9de0da0d58 100644
--- a/samples/server/petstore/java-play-framework/app/apimodels/Pet.java
+++ b/samples/server/petstore/java-play-framework/app/apimodels/Pet.java
@@ -25,7 +25,7 @@ public class Pet   {
   private List<String> photoUrls = new ArrayList<String>();
 
   @JsonProperty("tags")
-  private List<Tag> tags;
+  private List<Tag> tags = null;
 
   /**
    * pet status in the store
@@ -144,6 +144,9 @@ public class Pet   {
   }
 
   public Pet addTagsItem(Tag tagsItem) {
+    if (this.tags == null) {
+      this.tags = new ArrayList<Tag>();
+    }
     this.tags.add(tagsItem);
     return this;
   }
diff --git a/samples/server/petstore/jaxrs/jersey1/src/gen/java/io/swagger/model/AdditionalPropertiesClass.java b/samples/server/petstore/jaxrs/jersey1/src/gen/java/io/swagger/model/AdditionalPropertiesClass.java
index bf988ba5d4..e945e61897 100644
--- a/samples/server/petstore/jaxrs/jersey1/src/gen/java/io/swagger/model/AdditionalPropertiesClass.java
+++ b/samples/server/petstore/jaxrs/jersey1/src/gen/java/io/swagger/model/AdditionalPropertiesClass.java
@@ -40,6 +40,9 @@ public class AdditionalPropertiesClass   {
   }
 
   public AdditionalPropertiesClass putMapPropertyItem(String key, String mapPropertyItem) {
+    if (this.mapProperty == null) {
+      this.mapProperty = new HashMap<String, String>();
+    }
     this.mapProperty.put(key, mapPropertyItem);
     return this;
   }
@@ -64,6 +67,9 @@ public class AdditionalPropertiesClass   {
   }
 
   public AdditionalPropertiesClass putMapOfMapPropertyItem(String key, Map<String, String> mapOfMapPropertyItem) {
+    if (this.mapOfMapProperty == null) {
+      this.mapOfMapProperty = new HashMap<String, Map<String, String>>();
+    }
     this.mapOfMapProperty.put(key, mapOfMapPropertyItem);
     return this;
   }
diff --git a/samples/server/petstore/jaxrs/jersey1/src/gen/java/io/swagger/model/ArrayOfArrayOfNumberOnly.java b/samples/server/petstore/jaxrs/jersey1/src/gen/java/io/swagger/model/ArrayOfArrayOfNumberOnly.java
index 9df3539b9e..96ec13ad4f 100644
--- a/samples/server/petstore/jaxrs/jersey1/src/gen/java/io/swagger/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/server/petstore/jaxrs/jersey1/src/gen/java/io/swagger/model/ArrayOfArrayOfNumberOnly.java
@@ -37,6 +37,9 @@ public class ArrayOfArrayOfNumberOnly   {
   }
 
   public ArrayOfArrayOfNumberOnly addArrayArrayNumberItem(List<BigDecimal> arrayArrayNumberItem) {
+    if (this.arrayArrayNumber == null) {
+      this.arrayArrayNumber = new ArrayList<List<BigDecimal>>();
+    }
     this.arrayArrayNumber.add(arrayArrayNumberItem);
     return this;
   }
diff --git a/samples/server/petstore/jaxrs/jersey1/src/gen/java/io/swagger/model/ArrayOfNumberOnly.java b/samples/server/petstore/jaxrs/jersey1/src/gen/java/io/swagger/model/ArrayOfNumberOnly.java
index 80afcc9c40..e04487ba65 100644
--- a/samples/server/petstore/jaxrs/jersey1/src/gen/java/io/swagger/model/ArrayOfNumberOnly.java
+++ b/samples/server/petstore/jaxrs/jersey1/src/gen/java/io/swagger/model/ArrayOfNumberOnly.java
@@ -37,6 +37,9 @@ public class ArrayOfNumberOnly   {
   }
 
   public ArrayOfNumberOnly addArrayNumberItem(BigDecimal arrayNumberItem) {
+    if (this.arrayNumber == null) {
+      this.arrayNumber = new ArrayList<BigDecimal>();
+    }
     this.arrayNumber.add(arrayNumberItem);
     return this;
   }
diff --git a/samples/server/petstore/jaxrs/jersey1/src/gen/java/io/swagger/model/ArrayTest.java b/samples/server/petstore/jaxrs/jersey1/src/gen/java/io/swagger/model/ArrayTest.java
index 3b5e777759..6e391addfe 100644
--- a/samples/server/petstore/jaxrs/jersey1/src/gen/java/io/swagger/model/ArrayTest.java
+++ b/samples/server/petstore/jaxrs/jersey1/src/gen/java/io/swagger/model/ArrayTest.java
@@ -43,6 +43,9 @@ public class ArrayTest   {
   }
 
   public ArrayTest addArrayOfStringItem(String arrayOfStringItem) {
+    if (this.arrayOfString == null) {
+      this.arrayOfString = new ArrayList<String>();
+    }
     this.arrayOfString.add(arrayOfStringItem);
     return this;
   }
@@ -67,6 +70,9 @@ public class ArrayTest   {
   }
 
   public ArrayTest addArrayArrayOfIntegerItem(List<Long> arrayArrayOfIntegerItem) {
+    if (this.arrayArrayOfInteger == null) {
+      this.arrayArrayOfInteger = new ArrayList<List<Long>>();
+    }
     this.arrayArrayOfInteger.add(arrayArrayOfIntegerItem);
     return this;
   }
@@ -91,6 +97,9 @@ public class ArrayTest   {
   }
 
   public ArrayTest addArrayArrayOfModelItem(List<ReadOnlyFirst> arrayArrayOfModelItem) {
+    if (this.arrayArrayOfModel == null) {
+      this.arrayArrayOfModel = new ArrayList<List<ReadOnlyFirst>>();
+    }
     this.arrayArrayOfModel.add(arrayArrayOfModelItem);
     return this;
   }
diff --git a/samples/server/petstore/jaxrs/jersey1/src/gen/java/io/swagger/model/EnumArrays.java b/samples/server/petstore/jaxrs/jersey1/src/gen/java/io/swagger/model/EnumArrays.java
index f4f55cd1d6..a4fa1efac8 100644
--- a/samples/server/petstore/jaxrs/jersey1/src/gen/java/io/swagger/model/EnumArrays.java
+++ b/samples/server/petstore/jaxrs/jersey1/src/gen/java/io/swagger/model/EnumArrays.java
@@ -121,6 +121,9 @@ public class EnumArrays   {
   }
 
   public EnumArrays addArrayEnumItem(ArrayEnumEnum arrayEnumItem) {
+    if (this.arrayEnum == null) {
+      this.arrayEnum = new ArrayList<ArrayEnumEnum>();
+    }
     this.arrayEnum.add(arrayEnumItem);
     return this;
   }
diff --git a/samples/server/petstore/jaxrs/jersey1/src/gen/java/io/swagger/model/MapTest.java b/samples/server/petstore/jaxrs/jersey1/src/gen/java/io/swagger/model/MapTest.java
index 6d815004b2..c1625ac70b 100644
--- a/samples/server/petstore/jaxrs/jersey1/src/gen/java/io/swagger/model/MapTest.java
+++ b/samples/server/petstore/jaxrs/jersey1/src/gen/java/io/swagger/model/MapTest.java
@@ -72,6 +72,9 @@ public class MapTest   {
   }
 
   public MapTest putMapMapOfStringItem(String key, Map<String, String> mapMapOfStringItem) {
+    if (this.mapMapOfString == null) {
+      this.mapMapOfString = new HashMap<String, Map<String, String>>();
+    }
     this.mapMapOfString.put(key, mapMapOfStringItem);
     return this;
   }
@@ -96,6 +99,9 @@ public class MapTest   {
   }
 
   public MapTest putMapOfEnumStringItem(String key, InnerEnum mapOfEnumStringItem) {
+    if (this.mapOfEnumString == null) {
+      this.mapOfEnumString = new HashMap<String, InnerEnum>();
+    }
     this.mapOfEnumString.put(key, mapOfEnumStringItem);
     return this;
   }
diff --git a/samples/server/petstore/jaxrs/jersey1/src/gen/java/io/swagger/model/MixedPropertiesAndAdditionalPropertiesClass.java b/samples/server/petstore/jaxrs/jersey1/src/gen/java/io/swagger/model/MixedPropertiesAndAdditionalPropertiesClass.java
index 13ef25885b..85064283e4 100644
--- a/samples/server/petstore/jaxrs/jersey1/src/gen/java/io/swagger/model/MixedPropertiesAndAdditionalPropertiesClass.java
+++ b/samples/server/petstore/jaxrs/jersey1/src/gen/java/io/swagger/model/MixedPropertiesAndAdditionalPropertiesClass.java
@@ -84,6 +84,9 @@ public class MixedPropertiesAndAdditionalPropertiesClass   {
   }
 
   public MixedPropertiesAndAdditionalPropertiesClass putMapItem(String key, Animal mapItem) {
+    if (this.map == null) {
+      this.map = new HashMap<String, Animal>();
+    }
     this.map.put(key, mapItem);
     return this;
   }
diff --git a/samples/server/petstore/jaxrs/jersey1/src/gen/java/io/swagger/model/Pet.java b/samples/server/petstore/jaxrs/jersey1/src/gen/java/io/swagger/model/Pet.java
index 6d7174ae3e..dee942d257 100644
--- a/samples/server/petstore/jaxrs/jersey1/src/gen/java/io/swagger/model/Pet.java
+++ b/samples/server/petstore/jaxrs/jersey1/src/gen/java/io/swagger/model/Pet.java
@@ -170,6 +170,9 @@ public class Pet   {
   }
 
   public Pet addTagsItem(Tag tagsItem) {
+    if (this.tags == null) {
+      this.tags = new ArrayList<Tag>();
+    }
     this.tags.add(tagsItem);
     return this;
   }
diff --git a/samples/server/petstore/jaxrs/jersey2/src/gen/java/io/swagger/model/AdditionalPropertiesClass.java b/samples/server/petstore/jaxrs/jersey2/src/gen/java/io/swagger/model/AdditionalPropertiesClass.java
index bf988ba5d4..e945e61897 100644
--- a/samples/server/petstore/jaxrs/jersey2/src/gen/java/io/swagger/model/AdditionalPropertiesClass.java
+++ b/samples/server/petstore/jaxrs/jersey2/src/gen/java/io/swagger/model/AdditionalPropertiesClass.java
@@ -40,6 +40,9 @@ public class AdditionalPropertiesClass   {
   }
 
   public AdditionalPropertiesClass putMapPropertyItem(String key, String mapPropertyItem) {
+    if (this.mapProperty == null) {
+      this.mapProperty = new HashMap<String, String>();
+    }
     this.mapProperty.put(key, mapPropertyItem);
     return this;
   }
@@ -64,6 +67,9 @@ public class AdditionalPropertiesClass   {
   }
 
   public AdditionalPropertiesClass putMapOfMapPropertyItem(String key, Map<String, String> mapOfMapPropertyItem) {
+    if (this.mapOfMapProperty == null) {
+      this.mapOfMapProperty = new HashMap<String, Map<String, String>>();
+    }
     this.mapOfMapProperty.put(key, mapOfMapPropertyItem);
     return this;
   }
diff --git a/samples/server/petstore/jaxrs/jersey2/src/gen/java/io/swagger/model/ArrayOfArrayOfNumberOnly.java b/samples/server/petstore/jaxrs/jersey2/src/gen/java/io/swagger/model/ArrayOfArrayOfNumberOnly.java
index 9df3539b9e..96ec13ad4f 100644
--- a/samples/server/petstore/jaxrs/jersey2/src/gen/java/io/swagger/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/server/petstore/jaxrs/jersey2/src/gen/java/io/swagger/model/ArrayOfArrayOfNumberOnly.java
@@ -37,6 +37,9 @@ public class ArrayOfArrayOfNumberOnly   {
   }
 
   public ArrayOfArrayOfNumberOnly addArrayArrayNumberItem(List<BigDecimal> arrayArrayNumberItem) {
+    if (this.arrayArrayNumber == null) {
+      this.arrayArrayNumber = new ArrayList<List<BigDecimal>>();
+    }
     this.arrayArrayNumber.add(arrayArrayNumberItem);
     return this;
   }
diff --git a/samples/server/petstore/jaxrs/jersey2/src/gen/java/io/swagger/model/ArrayOfNumberOnly.java b/samples/server/petstore/jaxrs/jersey2/src/gen/java/io/swagger/model/ArrayOfNumberOnly.java
index 80afcc9c40..e04487ba65 100644
--- a/samples/server/petstore/jaxrs/jersey2/src/gen/java/io/swagger/model/ArrayOfNumberOnly.java
+++ b/samples/server/petstore/jaxrs/jersey2/src/gen/java/io/swagger/model/ArrayOfNumberOnly.java
@@ -37,6 +37,9 @@ public class ArrayOfNumberOnly   {
   }
 
   public ArrayOfNumberOnly addArrayNumberItem(BigDecimal arrayNumberItem) {
+    if (this.arrayNumber == null) {
+      this.arrayNumber = new ArrayList<BigDecimal>();
+    }
     this.arrayNumber.add(arrayNumberItem);
     return this;
   }
diff --git a/samples/server/petstore/jaxrs/jersey2/src/gen/java/io/swagger/model/ArrayTest.java b/samples/server/petstore/jaxrs/jersey2/src/gen/java/io/swagger/model/ArrayTest.java
index 3b5e777759..6e391addfe 100644
--- a/samples/server/petstore/jaxrs/jersey2/src/gen/java/io/swagger/model/ArrayTest.java
+++ b/samples/server/petstore/jaxrs/jersey2/src/gen/java/io/swagger/model/ArrayTest.java
@@ -43,6 +43,9 @@ public class ArrayTest   {
   }
 
   public ArrayTest addArrayOfStringItem(String arrayOfStringItem) {
+    if (this.arrayOfString == null) {
+      this.arrayOfString = new ArrayList<String>();
+    }
     this.arrayOfString.add(arrayOfStringItem);
     return this;
   }
@@ -67,6 +70,9 @@ public class ArrayTest   {
   }
 
   public ArrayTest addArrayArrayOfIntegerItem(List<Long> arrayArrayOfIntegerItem) {
+    if (this.arrayArrayOfInteger == null) {
+      this.arrayArrayOfInteger = new ArrayList<List<Long>>();
+    }
     this.arrayArrayOfInteger.add(arrayArrayOfIntegerItem);
     return this;
   }
@@ -91,6 +97,9 @@ public class ArrayTest   {
   }
 
   public ArrayTest addArrayArrayOfModelItem(List<ReadOnlyFirst> arrayArrayOfModelItem) {
+    if (this.arrayArrayOfModel == null) {
+      this.arrayArrayOfModel = new ArrayList<List<ReadOnlyFirst>>();
+    }
     this.arrayArrayOfModel.add(arrayArrayOfModelItem);
     return this;
   }
diff --git a/samples/server/petstore/jaxrs/jersey2/src/gen/java/io/swagger/model/EnumArrays.java b/samples/server/petstore/jaxrs/jersey2/src/gen/java/io/swagger/model/EnumArrays.java
index f4f55cd1d6..a4fa1efac8 100644
--- a/samples/server/petstore/jaxrs/jersey2/src/gen/java/io/swagger/model/EnumArrays.java
+++ b/samples/server/petstore/jaxrs/jersey2/src/gen/java/io/swagger/model/EnumArrays.java
@@ -121,6 +121,9 @@ public class EnumArrays   {
   }
 
   public EnumArrays addArrayEnumItem(ArrayEnumEnum arrayEnumItem) {
+    if (this.arrayEnum == null) {
+      this.arrayEnum = new ArrayList<ArrayEnumEnum>();
+    }
     this.arrayEnum.add(arrayEnumItem);
     return this;
   }
diff --git a/samples/server/petstore/jaxrs/jersey2/src/gen/java/io/swagger/model/MapTest.java b/samples/server/petstore/jaxrs/jersey2/src/gen/java/io/swagger/model/MapTest.java
index 6d815004b2..c1625ac70b 100644
--- a/samples/server/petstore/jaxrs/jersey2/src/gen/java/io/swagger/model/MapTest.java
+++ b/samples/server/petstore/jaxrs/jersey2/src/gen/java/io/swagger/model/MapTest.java
@@ -72,6 +72,9 @@ public class MapTest   {
   }
 
   public MapTest putMapMapOfStringItem(String key, Map<String, String> mapMapOfStringItem) {
+    if (this.mapMapOfString == null) {
+      this.mapMapOfString = new HashMap<String, Map<String, String>>();
+    }
     this.mapMapOfString.put(key, mapMapOfStringItem);
     return this;
   }
@@ -96,6 +99,9 @@ public class MapTest   {
   }
 
   public MapTest putMapOfEnumStringItem(String key, InnerEnum mapOfEnumStringItem) {
+    if (this.mapOfEnumString == null) {
+      this.mapOfEnumString = new HashMap<String, InnerEnum>();
+    }
     this.mapOfEnumString.put(key, mapOfEnumStringItem);
     return this;
   }
diff --git a/samples/server/petstore/jaxrs/jersey2/src/gen/java/io/swagger/model/MixedPropertiesAndAdditionalPropertiesClass.java b/samples/server/petstore/jaxrs/jersey2/src/gen/java/io/swagger/model/MixedPropertiesAndAdditionalPropertiesClass.java
index 13ef25885b..85064283e4 100644
--- a/samples/server/petstore/jaxrs/jersey2/src/gen/java/io/swagger/model/MixedPropertiesAndAdditionalPropertiesClass.java
+++ b/samples/server/petstore/jaxrs/jersey2/src/gen/java/io/swagger/model/MixedPropertiesAndAdditionalPropertiesClass.java
@@ -84,6 +84,9 @@ public class MixedPropertiesAndAdditionalPropertiesClass   {
   }
 
   public MixedPropertiesAndAdditionalPropertiesClass putMapItem(String key, Animal mapItem) {
+    if (this.map == null) {
+      this.map = new HashMap<String, Animal>();
+    }
     this.map.put(key, mapItem);
     return this;
   }
diff --git a/samples/server/petstore/jaxrs/jersey2/src/gen/java/io/swagger/model/Pet.java b/samples/server/petstore/jaxrs/jersey2/src/gen/java/io/swagger/model/Pet.java
index 6d7174ae3e..dee942d257 100644
--- a/samples/server/petstore/jaxrs/jersey2/src/gen/java/io/swagger/model/Pet.java
+++ b/samples/server/petstore/jaxrs/jersey2/src/gen/java/io/swagger/model/Pet.java
@@ -170,6 +170,9 @@ public class Pet   {
   }
 
   public Pet addTagsItem(Tag tagsItem) {
+    if (this.tags == null) {
+      this.tags = new ArrayList<Tag>();
+    }
     this.tags.add(tagsItem);
     return this;
   }
diff --git a/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/model/AdditionalPropertiesClass.java b/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/model/AdditionalPropertiesClass.java
index d05e148df5..f4cfcadae5 100644
--- a/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/model/AdditionalPropertiesClass.java
+++ b/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/model/AdditionalPropertiesClass.java
@@ -26,6 +26,9 @@ public class AdditionalPropertiesClass   {
   }
 
   public AdditionalPropertiesClass putMapPropertyItem(String key, String mapPropertyItem) {
+    if (this.mapProperty == null) {
+      this.mapProperty = new HashMap<String, String>();
+    }
     this.mapProperty.put(key, mapPropertyItem);
     return this;
   }
@@ -49,6 +52,9 @@ public class AdditionalPropertiesClass   {
   }
 
   public AdditionalPropertiesClass putMapOfMapPropertyItem(String key, Map<String, String> mapOfMapPropertyItem) {
+    if (this.mapOfMapProperty == null) {
+      this.mapOfMapProperty = new HashMap<String, Map<String, String>>();
+    }
     this.mapOfMapProperty.put(key, mapOfMapPropertyItem);
     return this;
   }
diff --git a/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/model/ArrayOfArrayOfNumberOnly.java b/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/model/ArrayOfArrayOfNumberOnly.java
index f60805cc02..8f975d8fed 100644
--- a/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/model/ArrayOfArrayOfNumberOnly.java
@@ -23,6 +23,9 @@ public class ArrayOfArrayOfNumberOnly   {
   }
 
   public ArrayOfArrayOfNumberOnly addArrayArrayNumberItem(List<BigDecimal> arrayArrayNumberItem) {
+    if (this.arrayArrayNumber == null) {
+      this.arrayArrayNumber = new ArrayList<List<BigDecimal>>();
+    }
     this.arrayArrayNumber.add(arrayArrayNumberItem);
     return this;
   }
diff --git a/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/model/ArrayOfNumberOnly.java b/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/model/ArrayOfNumberOnly.java
index d4f0f5010e..2c55600855 100644
--- a/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/model/ArrayOfNumberOnly.java
+++ b/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/model/ArrayOfNumberOnly.java
@@ -23,6 +23,9 @@ public class ArrayOfNumberOnly   {
   }
 
   public ArrayOfNumberOnly addArrayNumberItem(BigDecimal arrayNumberItem) {
+    if (this.arrayNumber == null) {
+      this.arrayNumber = new ArrayList<BigDecimal>();
+    }
     this.arrayNumber.add(arrayNumberItem);
     return this;
   }
diff --git a/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/model/ArrayTest.java b/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/model/ArrayTest.java
index 10c4c6c646..664e319cd3 100644
--- a/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/model/ArrayTest.java
+++ b/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/model/ArrayTest.java
@@ -29,6 +29,9 @@ public class ArrayTest   {
   }
 
   public ArrayTest addArrayOfStringItem(String arrayOfStringItem) {
+    if (this.arrayOfString == null) {
+      this.arrayOfString = new ArrayList<String>();
+    }
     this.arrayOfString.add(arrayOfStringItem);
     return this;
   }
@@ -52,6 +55,9 @@ public class ArrayTest   {
   }
 
   public ArrayTest addArrayArrayOfIntegerItem(List<Long> arrayArrayOfIntegerItem) {
+    if (this.arrayArrayOfInteger == null) {
+      this.arrayArrayOfInteger = new ArrayList<List<Long>>();
+    }
     this.arrayArrayOfInteger.add(arrayArrayOfIntegerItem);
     return this;
   }
@@ -75,6 +81,9 @@ public class ArrayTest   {
   }
 
   public ArrayTest addArrayArrayOfModelItem(List<ReadOnlyFirst> arrayArrayOfModelItem) {
+    if (this.arrayArrayOfModel == null) {
+      this.arrayArrayOfModel = new ArrayList<List<ReadOnlyFirst>>();
+    }
     this.arrayArrayOfModel.add(arrayArrayOfModelItem);
     return this;
   }
diff --git a/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/model/EnumArrays.java b/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/model/EnumArrays.java
index 06bb785ce0..f904035e48 100644
--- a/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/model/EnumArrays.java
+++ b/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/model/EnumArrays.java
@@ -106,6 +106,9 @@ public class EnumArrays   {
   }
 
   public EnumArrays addArrayEnumItem(ArrayEnumEnum arrayEnumItem) {
+    if (this.arrayEnum == null) {
+      this.arrayEnum = new ArrayList<ArrayEnumEnum>();
+    }
     this.arrayEnum.add(arrayEnumItem);
     return this;
   }
diff --git a/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/model/MapTest.java b/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/model/MapTest.java
index 9b6fc7acef..434c3a8f1b 100644
--- a/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/model/MapTest.java
+++ b/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/model/MapTest.java
@@ -58,6 +58,9 @@ public class MapTest   {
   }
 
   public MapTest putMapMapOfStringItem(String key, Map<String, String> mapMapOfStringItem) {
+    if (this.mapMapOfString == null) {
+      this.mapMapOfString = new HashMap<String, Map<String, String>>();
+    }
     this.mapMapOfString.put(key, mapMapOfStringItem);
     return this;
   }
@@ -81,6 +84,9 @@ public class MapTest   {
   }
 
   public MapTest putMapOfEnumStringItem(String key, InnerEnum mapOfEnumStringItem) {
+    if (this.mapOfEnumString == null) {
+      this.mapOfEnumString = new HashMap<String, InnerEnum>();
+    }
     this.mapOfEnumString.put(key, mapOfEnumStringItem);
     return this;
   }
diff --git a/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/model/MixedPropertiesAndAdditionalPropertiesClass.java b/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/model/MixedPropertiesAndAdditionalPropertiesClass.java
index 93ec3584fa..727205e40f 100644
--- a/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/model/MixedPropertiesAndAdditionalPropertiesClass.java
+++ b/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/model/MixedPropertiesAndAdditionalPropertiesClass.java
@@ -68,6 +68,9 @@ public class MixedPropertiesAndAdditionalPropertiesClass   {
   }
 
   public MixedPropertiesAndAdditionalPropertiesClass putMapItem(String key, Animal mapItem) {
+    if (this.map == null) {
+      this.map = new HashMap<String, Animal>();
+    }
     this.map.put(key, mapItem);
     return this;
   }
diff --git a/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/model/Pet.java b/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/model/Pet.java
index 566cbc43a6..b013846b4d 100644
--- a/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/model/Pet.java
+++ b/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/model/Pet.java
@@ -152,6 +152,9 @@ public class Pet   {
   }
 
   public Pet addTagsItem(Tag tagsItem) {
+    if (this.tags == null) {
+      this.tags = new ArrayList<Tag>();
+    }
     this.tags.add(tagsItem);
     return this;
   }
diff --git a/samples/server/petstore/spring-mvc/src/main/java/io/swagger/model/AdditionalPropertiesClass.java b/samples/server/petstore/spring-mvc/src/main/java/io/swagger/model/AdditionalPropertiesClass.java
index d05e148df5..f4cfcadae5 100644
--- a/samples/server/petstore/spring-mvc/src/main/java/io/swagger/model/AdditionalPropertiesClass.java
+++ b/samples/server/petstore/spring-mvc/src/main/java/io/swagger/model/AdditionalPropertiesClass.java
@@ -26,6 +26,9 @@ public class AdditionalPropertiesClass   {
   }
 
   public AdditionalPropertiesClass putMapPropertyItem(String key, String mapPropertyItem) {
+    if (this.mapProperty == null) {
+      this.mapProperty = new HashMap<String, String>();
+    }
     this.mapProperty.put(key, mapPropertyItem);
     return this;
   }
@@ -49,6 +52,9 @@ public class AdditionalPropertiesClass   {
   }
 
   public AdditionalPropertiesClass putMapOfMapPropertyItem(String key, Map<String, String> mapOfMapPropertyItem) {
+    if (this.mapOfMapProperty == null) {
+      this.mapOfMapProperty = new HashMap<String, Map<String, String>>();
+    }
     this.mapOfMapProperty.put(key, mapOfMapPropertyItem);
     return this;
   }
diff --git a/samples/server/petstore/spring-mvc/src/main/java/io/swagger/model/ArrayOfArrayOfNumberOnly.java b/samples/server/petstore/spring-mvc/src/main/java/io/swagger/model/ArrayOfArrayOfNumberOnly.java
index f60805cc02..8f975d8fed 100644
--- a/samples/server/petstore/spring-mvc/src/main/java/io/swagger/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/server/petstore/spring-mvc/src/main/java/io/swagger/model/ArrayOfArrayOfNumberOnly.java
@@ -23,6 +23,9 @@ public class ArrayOfArrayOfNumberOnly   {
   }
 
   public ArrayOfArrayOfNumberOnly addArrayArrayNumberItem(List<BigDecimal> arrayArrayNumberItem) {
+    if (this.arrayArrayNumber == null) {
+      this.arrayArrayNumber = new ArrayList<List<BigDecimal>>();
+    }
     this.arrayArrayNumber.add(arrayArrayNumberItem);
     return this;
   }
diff --git a/samples/server/petstore/spring-mvc/src/main/java/io/swagger/model/ArrayOfNumberOnly.java b/samples/server/petstore/spring-mvc/src/main/java/io/swagger/model/ArrayOfNumberOnly.java
index d4f0f5010e..2c55600855 100644
--- a/samples/server/petstore/spring-mvc/src/main/java/io/swagger/model/ArrayOfNumberOnly.java
+++ b/samples/server/petstore/spring-mvc/src/main/java/io/swagger/model/ArrayOfNumberOnly.java
@@ -23,6 +23,9 @@ public class ArrayOfNumberOnly   {
   }
 
   public ArrayOfNumberOnly addArrayNumberItem(BigDecimal arrayNumberItem) {
+    if (this.arrayNumber == null) {
+      this.arrayNumber = new ArrayList<BigDecimal>();
+    }
     this.arrayNumber.add(arrayNumberItem);
     return this;
   }
diff --git a/samples/server/petstore/spring-mvc/src/main/java/io/swagger/model/ArrayTest.java b/samples/server/petstore/spring-mvc/src/main/java/io/swagger/model/ArrayTest.java
index 10c4c6c646..664e319cd3 100644
--- a/samples/server/petstore/spring-mvc/src/main/java/io/swagger/model/ArrayTest.java
+++ b/samples/server/petstore/spring-mvc/src/main/java/io/swagger/model/ArrayTest.java
@@ -29,6 +29,9 @@ public class ArrayTest   {
   }
 
   public ArrayTest addArrayOfStringItem(String arrayOfStringItem) {
+    if (this.arrayOfString == null) {
+      this.arrayOfString = new ArrayList<String>();
+    }
     this.arrayOfString.add(arrayOfStringItem);
     return this;
   }
@@ -52,6 +55,9 @@ public class ArrayTest   {
   }
 
   public ArrayTest addArrayArrayOfIntegerItem(List<Long> arrayArrayOfIntegerItem) {
+    if (this.arrayArrayOfInteger == null) {
+      this.arrayArrayOfInteger = new ArrayList<List<Long>>();
+    }
     this.arrayArrayOfInteger.add(arrayArrayOfIntegerItem);
     return this;
   }
@@ -75,6 +81,9 @@ public class ArrayTest   {
   }
 
   public ArrayTest addArrayArrayOfModelItem(List<ReadOnlyFirst> arrayArrayOfModelItem) {
+    if (this.arrayArrayOfModel == null) {
+      this.arrayArrayOfModel = new ArrayList<List<ReadOnlyFirst>>();
+    }
     this.arrayArrayOfModel.add(arrayArrayOfModelItem);
     return this;
   }
diff --git a/samples/server/petstore/spring-mvc/src/main/java/io/swagger/model/EnumArrays.java b/samples/server/petstore/spring-mvc/src/main/java/io/swagger/model/EnumArrays.java
index 06bb785ce0..f904035e48 100644
--- a/samples/server/petstore/spring-mvc/src/main/java/io/swagger/model/EnumArrays.java
+++ b/samples/server/petstore/spring-mvc/src/main/java/io/swagger/model/EnumArrays.java
@@ -106,6 +106,9 @@ public class EnumArrays   {
   }
 
   public EnumArrays addArrayEnumItem(ArrayEnumEnum arrayEnumItem) {
+    if (this.arrayEnum == null) {
+      this.arrayEnum = new ArrayList<ArrayEnumEnum>();
+    }
     this.arrayEnum.add(arrayEnumItem);
     return this;
   }
diff --git a/samples/server/petstore/spring-mvc/src/main/java/io/swagger/model/MapTest.java b/samples/server/petstore/spring-mvc/src/main/java/io/swagger/model/MapTest.java
index 9b6fc7acef..434c3a8f1b 100644
--- a/samples/server/petstore/spring-mvc/src/main/java/io/swagger/model/MapTest.java
+++ b/samples/server/petstore/spring-mvc/src/main/java/io/swagger/model/MapTest.java
@@ -58,6 +58,9 @@ public class MapTest   {
   }
 
   public MapTest putMapMapOfStringItem(String key, Map<String, String> mapMapOfStringItem) {
+    if (this.mapMapOfString == null) {
+      this.mapMapOfString = new HashMap<String, Map<String, String>>();
+    }
     this.mapMapOfString.put(key, mapMapOfStringItem);
     return this;
   }
@@ -81,6 +84,9 @@ public class MapTest   {
   }
 
   public MapTest putMapOfEnumStringItem(String key, InnerEnum mapOfEnumStringItem) {
+    if (this.mapOfEnumString == null) {
+      this.mapOfEnumString = new HashMap<String, InnerEnum>();
+    }
     this.mapOfEnumString.put(key, mapOfEnumStringItem);
     return this;
   }
diff --git a/samples/server/petstore/spring-mvc/src/main/java/io/swagger/model/MixedPropertiesAndAdditionalPropertiesClass.java b/samples/server/petstore/spring-mvc/src/main/java/io/swagger/model/MixedPropertiesAndAdditionalPropertiesClass.java
index 66e8b53b9b..dba1241f6d 100644
--- a/samples/server/petstore/spring-mvc/src/main/java/io/swagger/model/MixedPropertiesAndAdditionalPropertiesClass.java
+++ b/samples/server/petstore/spring-mvc/src/main/java/io/swagger/model/MixedPropertiesAndAdditionalPropertiesClass.java
@@ -68,6 +68,9 @@ public class MixedPropertiesAndAdditionalPropertiesClass   {
   }
 
   public MixedPropertiesAndAdditionalPropertiesClass putMapItem(String key, Animal mapItem) {
+    if (this.map == null) {
+      this.map = new HashMap<String, Animal>();
+    }
     this.map.put(key, mapItem);
     return this;
   }
diff --git a/samples/server/petstore/spring-mvc/src/main/java/io/swagger/model/Pet.java b/samples/server/petstore/spring-mvc/src/main/java/io/swagger/model/Pet.java
index 566cbc43a6..b013846b4d 100644
--- a/samples/server/petstore/spring-mvc/src/main/java/io/swagger/model/Pet.java
+++ b/samples/server/petstore/spring-mvc/src/main/java/io/swagger/model/Pet.java
@@ -152,6 +152,9 @@ public class Pet   {
   }
 
   public Pet addTagsItem(Tag tagsItem) {
+    if (this.tags == null) {
+      this.tags = new ArrayList<Tag>();
+    }
     this.tags.add(tagsItem);
     return this;
   }
diff --git a/samples/server/petstore/springboot-delegate-j8/src/main/java/io/swagger/model/AdditionalPropertiesClass.java b/samples/server/petstore/springboot-delegate-j8/src/main/java/io/swagger/model/AdditionalPropertiesClass.java
index d05e148df5..f4cfcadae5 100644
--- a/samples/server/petstore/springboot-delegate-j8/src/main/java/io/swagger/model/AdditionalPropertiesClass.java
+++ b/samples/server/petstore/springboot-delegate-j8/src/main/java/io/swagger/model/AdditionalPropertiesClass.java
@@ -26,6 +26,9 @@ public class AdditionalPropertiesClass   {
   }
 
   public AdditionalPropertiesClass putMapPropertyItem(String key, String mapPropertyItem) {
+    if (this.mapProperty == null) {
+      this.mapProperty = new HashMap<String, String>();
+    }
     this.mapProperty.put(key, mapPropertyItem);
     return this;
   }
@@ -49,6 +52,9 @@ public class AdditionalPropertiesClass   {
   }
 
   public AdditionalPropertiesClass putMapOfMapPropertyItem(String key, Map<String, String> mapOfMapPropertyItem) {
+    if (this.mapOfMapProperty == null) {
+      this.mapOfMapProperty = new HashMap<String, Map<String, String>>();
+    }
     this.mapOfMapProperty.put(key, mapOfMapPropertyItem);
     return this;
   }
diff --git a/samples/server/petstore/springboot-delegate-j8/src/main/java/io/swagger/model/ArrayOfArrayOfNumberOnly.java b/samples/server/petstore/springboot-delegate-j8/src/main/java/io/swagger/model/ArrayOfArrayOfNumberOnly.java
index f60805cc02..8f975d8fed 100644
--- a/samples/server/petstore/springboot-delegate-j8/src/main/java/io/swagger/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/server/petstore/springboot-delegate-j8/src/main/java/io/swagger/model/ArrayOfArrayOfNumberOnly.java
@@ -23,6 +23,9 @@ public class ArrayOfArrayOfNumberOnly   {
   }
 
   public ArrayOfArrayOfNumberOnly addArrayArrayNumberItem(List<BigDecimal> arrayArrayNumberItem) {
+    if (this.arrayArrayNumber == null) {
+      this.arrayArrayNumber = new ArrayList<List<BigDecimal>>();
+    }
     this.arrayArrayNumber.add(arrayArrayNumberItem);
     return this;
   }
diff --git a/samples/server/petstore/springboot-delegate-j8/src/main/java/io/swagger/model/ArrayOfNumberOnly.java b/samples/server/petstore/springboot-delegate-j8/src/main/java/io/swagger/model/ArrayOfNumberOnly.java
index d4f0f5010e..2c55600855 100644
--- a/samples/server/petstore/springboot-delegate-j8/src/main/java/io/swagger/model/ArrayOfNumberOnly.java
+++ b/samples/server/petstore/springboot-delegate-j8/src/main/java/io/swagger/model/ArrayOfNumberOnly.java
@@ -23,6 +23,9 @@ public class ArrayOfNumberOnly   {
   }
 
   public ArrayOfNumberOnly addArrayNumberItem(BigDecimal arrayNumberItem) {
+    if (this.arrayNumber == null) {
+      this.arrayNumber = new ArrayList<BigDecimal>();
+    }
     this.arrayNumber.add(arrayNumberItem);
     return this;
   }
diff --git a/samples/server/petstore/springboot-delegate-j8/src/main/java/io/swagger/model/ArrayTest.java b/samples/server/petstore/springboot-delegate-j8/src/main/java/io/swagger/model/ArrayTest.java
index 10c4c6c646..664e319cd3 100644
--- a/samples/server/petstore/springboot-delegate-j8/src/main/java/io/swagger/model/ArrayTest.java
+++ b/samples/server/petstore/springboot-delegate-j8/src/main/java/io/swagger/model/ArrayTest.java
@@ -29,6 +29,9 @@ public class ArrayTest   {
   }
 
   public ArrayTest addArrayOfStringItem(String arrayOfStringItem) {
+    if (this.arrayOfString == null) {
+      this.arrayOfString = new ArrayList<String>();
+    }
     this.arrayOfString.add(arrayOfStringItem);
     return this;
   }
@@ -52,6 +55,9 @@ public class ArrayTest   {
   }
 
   public ArrayTest addArrayArrayOfIntegerItem(List<Long> arrayArrayOfIntegerItem) {
+    if (this.arrayArrayOfInteger == null) {
+      this.arrayArrayOfInteger = new ArrayList<List<Long>>();
+    }
     this.arrayArrayOfInteger.add(arrayArrayOfIntegerItem);
     return this;
   }
@@ -75,6 +81,9 @@ public class ArrayTest   {
   }
 
   public ArrayTest addArrayArrayOfModelItem(List<ReadOnlyFirst> arrayArrayOfModelItem) {
+    if (this.arrayArrayOfModel == null) {
+      this.arrayArrayOfModel = new ArrayList<List<ReadOnlyFirst>>();
+    }
     this.arrayArrayOfModel.add(arrayArrayOfModelItem);
     return this;
   }
diff --git a/samples/server/petstore/springboot-delegate-j8/src/main/java/io/swagger/model/EnumArrays.java b/samples/server/petstore/springboot-delegate-j8/src/main/java/io/swagger/model/EnumArrays.java
index 06bb785ce0..f904035e48 100644
--- a/samples/server/petstore/springboot-delegate-j8/src/main/java/io/swagger/model/EnumArrays.java
+++ b/samples/server/petstore/springboot-delegate-j8/src/main/java/io/swagger/model/EnumArrays.java
@@ -106,6 +106,9 @@ public class EnumArrays   {
   }
 
   public EnumArrays addArrayEnumItem(ArrayEnumEnum arrayEnumItem) {
+    if (this.arrayEnum == null) {
+      this.arrayEnum = new ArrayList<ArrayEnumEnum>();
+    }
     this.arrayEnum.add(arrayEnumItem);
     return this;
   }
diff --git a/samples/server/petstore/springboot-delegate-j8/src/main/java/io/swagger/model/MapTest.java b/samples/server/petstore/springboot-delegate-j8/src/main/java/io/swagger/model/MapTest.java
index 9b6fc7acef..434c3a8f1b 100644
--- a/samples/server/petstore/springboot-delegate-j8/src/main/java/io/swagger/model/MapTest.java
+++ b/samples/server/petstore/springboot-delegate-j8/src/main/java/io/swagger/model/MapTest.java
@@ -58,6 +58,9 @@ public class MapTest   {
   }
 
   public MapTest putMapMapOfStringItem(String key, Map<String, String> mapMapOfStringItem) {
+    if (this.mapMapOfString == null) {
+      this.mapMapOfString = new HashMap<String, Map<String, String>>();
+    }
     this.mapMapOfString.put(key, mapMapOfStringItem);
     return this;
   }
@@ -81,6 +84,9 @@ public class MapTest   {
   }
 
   public MapTest putMapOfEnumStringItem(String key, InnerEnum mapOfEnumStringItem) {
+    if (this.mapOfEnumString == null) {
+      this.mapOfEnumString = new HashMap<String, InnerEnum>();
+    }
     this.mapOfEnumString.put(key, mapOfEnumStringItem);
     return this;
   }
diff --git a/samples/server/petstore/springboot-delegate-j8/src/main/java/io/swagger/model/MixedPropertiesAndAdditionalPropertiesClass.java b/samples/server/petstore/springboot-delegate-j8/src/main/java/io/swagger/model/MixedPropertiesAndAdditionalPropertiesClass.java
index 93ec3584fa..727205e40f 100644
--- a/samples/server/petstore/springboot-delegate-j8/src/main/java/io/swagger/model/MixedPropertiesAndAdditionalPropertiesClass.java
+++ b/samples/server/petstore/springboot-delegate-j8/src/main/java/io/swagger/model/MixedPropertiesAndAdditionalPropertiesClass.java
@@ -68,6 +68,9 @@ public class MixedPropertiesAndAdditionalPropertiesClass   {
   }
 
   public MixedPropertiesAndAdditionalPropertiesClass putMapItem(String key, Animal mapItem) {
+    if (this.map == null) {
+      this.map = new HashMap<String, Animal>();
+    }
     this.map.put(key, mapItem);
     return this;
   }
diff --git a/samples/server/petstore/springboot-delegate-j8/src/main/java/io/swagger/model/Pet.java b/samples/server/petstore/springboot-delegate-j8/src/main/java/io/swagger/model/Pet.java
index 566cbc43a6..b013846b4d 100644
--- a/samples/server/petstore/springboot-delegate-j8/src/main/java/io/swagger/model/Pet.java
+++ b/samples/server/petstore/springboot-delegate-j8/src/main/java/io/swagger/model/Pet.java
@@ -152,6 +152,9 @@ public class Pet   {
   }
 
   public Pet addTagsItem(Tag tagsItem) {
+    if (this.tags == null) {
+      this.tags = new ArrayList<Tag>();
+    }
     this.tags.add(tagsItem);
     return this;
   }
diff --git a/samples/server/petstore/springboot-delegate/src/main/java/io/swagger/model/AdditionalPropertiesClass.java b/samples/server/petstore/springboot-delegate/src/main/java/io/swagger/model/AdditionalPropertiesClass.java
index d05e148df5..f4cfcadae5 100644
--- a/samples/server/petstore/springboot-delegate/src/main/java/io/swagger/model/AdditionalPropertiesClass.java
+++ b/samples/server/petstore/springboot-delegate/src/main/java/io/swagger/model/AdditionalPropertiesClass.java
@@ -26,6 +26,9 @@ public class AdditionalPropertiesClass   {
   }
 
   public AdditionalPropertiesClass putMapPropertyItem(String key, String mapPropertyItem) {
+    if (this.mapProperty == null) {
+      this.mapProperty = new HashMap<String, String>();
+    }
     this.mapProperty.put(key, mapPropertyItem);
     return this;
   }
@@ -49,6 +52,9 @@ public class AdditionalPropertiesClass   {
   }
 
   public AdditionalPropertiesClass putMapOfMapPropertyItem(String key, Map<String, String> mapOfMapPropertyItem) {
+    if (this.mapOfMapProperty == null) {
+      this.mapOfMapProperty = new HashMap<String, Map<String, String>>();
+    }
     this.mapOfMapProperty.put(key, mapOfMapPropertyItem);
     return this;
   }
diff --git a/samples/server/petstore/springboot-delegate/src/main/java/io/swagger/model/ArrayOfArrayOfNumberOnly.java b/samples/server/petstore/springboot-delegate/src/main/java/io/swagger/model/ArrayOfArrayOfNumberOnly.java
index f60805cc02..8f975d8fed 100644
--- a/samples/server/petstore/springboot-delegate/src/main/java/io/swagger/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/server/petstore/springboot-delegate/src/main/java/io/swagger/model/ArrayOfArrayOfNumberOnly.java
@@ -23,6 +23,9 @@ public class ArrayOfArrayOfNumberOnly   {
   }
 
   public ArrayOfArrayOfNumberOnly addArrayArrayNumberItem(List<BigDecimal> arrayArrayNumberItem) {
+    if (this.arrayArrayNumber == null) {
+      this.arrayArrayNumber = new ArrayList<List<BigDecimal>>();
+    }
     this.arrayArrayNumber.add(arrayArrayNumberItem);
     return this;
   }
diff --git a/samples/server/petstore/springboot-delegate/src/main/java/io/swagger/model/ArrayOfNumberOnly.java b/samples/server/petstore/springboot-delegate/src/main/java/io/swagger/model/ArrayOfNumberOnly.java
index d4f0f5010e..2c55600855 100644
--- a/samples/server/petstore/springboot-delegate/src/main/java/io/swagger/model/ArrayOfNumberOnly.java
+++ b/samples/server/petstore/springboot-delegate/src/main/java/io/swagger/model/ArrayOfNumberOnly.java
@@ -23,6 +23,9 @@ public class ArrayOfNumberOnly   {
   }
 
   public ArrayOfNumberOnly addArrayNumberItem(BigDecimal arrayNumberItem) {
+    if (this.arrayNumber == null) {
+      this.arrayNumber = new ArrayList<BigDecimal>();
+    }
     this.arrayNumber.add(arrayNumberItem);
     return this;
   }
diff --git a/samples/server/petstore/springboot-delegate/src/main/java/io/swagger/model/ArrayTest.java b/samples/server/petstore/springboot-delegate/src/main/java/io/swagger/model/ArrayTest.java
index 10c4c6c646..664e319cd3 100644
--- a/samples/server/petstore/springboot-delegate/src/main/java/io/swagger/model/ArrayTest.java
+++ b/samples/server/petstore/springboot-delegate/src/main/java/io/swagger/model/ArrayTest.java
@@ -29,6 +29,9 @@ public class ArrayTest   {
   }
 
   public ArrayTest addArrayOfStringItem(String arrayOfStringItem) {
+    if (this.arrayOfString == null) {
+      this.arrayOfString = new ArrayList<String>();
+    }
     this.arrayOfString.add(arrayOfStringItem);
     return this;
   }
@@ -52,6 +55,9 @@ public class ArrayTest   {
   }
 
   public ArrayTest addArrayArrayOfIntegerItem(List<Long> arrayArrayOfIntegerItem) {
+    if (this.arrayArrayOfInteger == null) {
+      this.arrayArrayOfInteger = new ArrayList<List<Long>>();
+    }
     this.arrayArrayOfInteger.add(arrayArrayOfIntegerItem);
     return this;
   }
@@ -75,6 +81,9 @@ public class ArrayTest   {
   }
 
   public ArrayTest addArrayArrayOfModelItem(List<ReadOnlyFirst> arrayArrayOfModelItem) {
+    if (this.arrayArrayOfModel == null) {
+      this.arrayArrayOfModel = new ArrayList<List<ReadOnlyFirst>>();
+    }
     this.arrayArrayOfModel.add(arrayArrayOfModelItem);
     return this;
   }
diff --git a/samples/server/petstore/springboot-delegate/src/main/java/io/swagger/model/EnumArrays.java b/samples/server/petstore/springboot-delegate/src/main/java/io/swagger/model/EnumArrays.java
index 06bb785ce0..f904035e48 100644
--- a/samples/server/petstore/springboot-delegate/src/main/java/io/swagger/model/EnumArrays.java
+++ b/samples/server/petstore/springboot-delegate/src/main/java/io/swagger/model/EnumArrays.java
@@ -106,6 +106,9 @@ public class EnumArrays   {
   }
 
   public EnumArrays addArrayEnumItem(ArrayEnumEnum arrayEnumItem) {
+    if (this.arrayEnum == null) {
+      this.arrayEnum = new ArrayList<ArrayEnumEnum>();
+    }
     this.arrayEnum.add(arrayEnumItem);
     return this;
   }
diff --git a/samples/server/petstore/springboot-delegate/src/main/java/io/swagger/model/MapTest.java b/samples/server/petstore/springboot-delegate/src/main/java/io/swagger/model/MapTest.java
index 9b6fc7acef..434c3a8f1b 100644
--- a/samples/server/petstore/springboot-delegate/src/main/java/io/swagger/model/MapTest.java
+++ b/samples/server/petstore/springboot-delegate/src/main/java/io/swagger/model/MapTest.java
@@ -58,6 +58,9 @@ public class MapTest   {
   }
 
   public MapTest putMapMapOfStringItem(String key, Map<String, String> mapMapOfStringItem) {
+    if (this.mapMapOfString == null) {
+      this.mapMapOfString = new HashMap<String, Map<String, String>>();
+    }
     this.mapMapOfString.put(key, mapMapOfStringItem);
     return this;
   }
@@ -81,6 +84,9 @@ public class MapTest   {
   }
 
   public MapTest putMapOfEnumStringItem(String key, InnerEnum mapOfEnumStringItem) {
+    if (this.mapOfEnumString == null) {
+      this.mapOfEnumString = new HashMap<String, InnerEnum>();
+    }
     this.mapOfEnumString.put(key, mapOfEnumStringItem);
     return this;
   }
diff --git a/samples/server/petstore/springboot-delegate/src/main/java/io/swagger/model/MixedPropertiesAndAdditionalPropertiesClass.java b/samples/server/petstore/springboot-delegate/src/main/java/io/swagger/model/MixedPropertiesAndAdditionalPropertiesClass.java
index 66e8b53b9b..dba1241f6d 100644
--- a/samples/server/petstore/springboot-delegate/src/main/java/io/swagger/model/MixedPropertiesAndAdditionalPropertiesClass.java
+++ b/samples/server/petstore/springboot-delegate/src/main/java/io/swagger/model/MixedPropertiesAndAdditionalPropertiesClass.java
@@ -68,6 +68,9 @@ public class MixedPropertiesAndAdditionalPropertiesClass   {
   }
 
   public MixedPropertiesAndAdditionalPropertiesClass putMapItem(String key, Animal mapItem) {
+    if (this.map == null) {
+      this.map = new HashMap<String, Animal>();
+    }
     this.map.put(key, mapItem);
     return this;
   }
diff --git a/samples/server/petstore/springboot-delegate/src/main/java/io/swagger/model/Pet.java b/samples/server/petstore/springboot-delegate/src/main/java/io/swagger/model/Pet.java
index 566cbc43a6..b013846b4d 100644
--- a/samples/server/petstore/springboot-delegate/src/main/java/io/swagger/model/Pet.java
+++ b/samples/server/petstore/springboot-delegate/src/main/java/io/swagger/model/Pet.java
@@ -152,6 +152,9 @@ public class Pet   {
   }
 
   public Pet addTagsItem(Tag tagsItem) {
+    if (this.tags == null) {
+      this.tags = new ArrayList<Tag>();
+    }
     this.tags.add(tagsItem);
     return this;
   }
diff --git a/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/api/FakeApi.java b/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/api/FakeApi.java
index 2d94861f66..602c5a1066 100644
--- a/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/api/FakeApi.java
+++ b/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/api/FakeApi.java
@@ -48,7 +48,7 @@ public interface FakeApi {
         produces = { "application/xml; charset=utf-8", "application/json; charset=utf-8" }, 
         consumes = { "application/xml; charset=utf-8", "application/json; charset=utf-8" },
         method = RequestMethod.POST)
-    ResponseEntity<Void> testEndpointParameters(@ApiParam(value = "None", required=true ) @RequestPart(value="number", required=true)  BigDecimal number,@ApiParam(value = "None", required=true ) @RequestPart(value="double", required=true)  Double _double,@ApiParam(value = "None", required=true ) @RequestPart(value="pattern_without_delimiter", required=true)  String patternWithoutDelimiter,@ApiParam(value = "None", required=true ) @RequestPart(value="byte", required=true)  byte[] _byte,@ApiParam(value = "None" ) @RequestPart(value="integer", required=false)  Integer integer,@ApiParam(value = "None" ) @RequestPart(value="int32", required=false)  Integer int32,@ApiParam(value = "None" ) @RequestPart(value="int64", required=false)  Long int64,@ApiParam(value = "None" ) @RequestPart(value="float", required=false)  Float _float,@ApiParam(value = "None" ) @RequestPart(value="string", required=false)  String string,@ApiParam(value = "None" ) @RequestPart(value="binary", required=false)  byte[] binary,@ApiParam(value = "None" ) @RequestPart(value="date", required=false)  LocalDate date,@ApiParam(value = "None" ) @RequestPart(value="dateTime", required=false)  DateTime dateTime,@ApiParam(value = "None" ) @RequestPart(value="password", required=false)  String password,@ApiParam(value = "None" ) @RequestPart(value="callback", required=false)  String paramCallback);
+    ResponseEntity<Void> testEndpointParameters(@ApiParam(value = "None", required=true) @RequestPart(value="number", required=true)  BigDecimal number,@ApiParam(value = "None", required=true) @RequestPart(value="double", required=true)  Double _double,@ApiParam(value = "None", required=true) @RequestPart(value="pattern_without_delimiter", required=true)  String patternWithoutDelimiter,@ApiParam(value = "None", required=true) @RequestPart(value="byte", required=true)  byte[] _byte,@ApiParam(value = "None") @RequestPart(value="integer", required=false)  Integer integer,@ApiParam(value = "None") @RequestPart(value="int32", required=false)  Integer int32,@ApiParam(value = "None") @RequestPart(value="int64", required=false)  Long int64,@ApiParam(value = "None") @RequestPart(value="float", required=false)  Float _float,@ApiParam(value = "None") @RequestPart(value="string", required=false)  String string,@ApiParam(value = "None") @RequestPart(value="binary", required=false)  byte[] binary,@ApiParam(value = "None") @RequestPart(value="date", required=false)  LocalDate date,@ApiParam(value = "None") @RequestPart(value="dateTime", required=false)  DateTime dateTime,@ApiParam(value = "None") @RequestPart(value="password", required=false)  String password,@ApiParam(value = "None") @RequestPart(value="callback", required=false)  String paramCallback);
 
 
     @ApiOperation(value = "To test enum parameters", notes = "To test enum parameters", response = Void.class, tags={ "fake", })
@@ -62,6 +62,6 @@ public interface FakeApi {
         produces = { "*/*" }, 
         consumes = { "*/*" },
         method = RequestMethod.GET)
-    ResponseEntity<Void> testEnumParameters(@ApiParam(value = "Form parameter enum test (string array)" , allowableValues="GREATER_THAN, DOLLAR") @RequestPart(value="enum_form_string_array", required=false)  List<String> enumFormStringArray,@ApiParam(value = "Form parameter enum test (string)" , allowableValues="_ABC, _EFG, _XYZ_", defaultValue="-efg") @RequestPart(value="enum_form_string", required=false)  String enumFormString, @ApiParam(value = "Query parameter enum test (string array)", allowableValues = "GREATER_THAN, DOLLAR") @RequestParam(value = "enum_query_string_array", required = false) List<String> enumQueryStringArray, @ApiParam(value = "Query parameter enum test (string)", allowableValues = "_ABC, _EFG, _XYZ_", defaultValue = "-efg") @RequestParam(value = "enum_query_string", required = false, defaultValue="-efg") String enumQueryString, @ApiParam(value = "Query parameter enum test (double)", allowableValues = "NUMBER_1, NUMBER_MINUS_2") @RequestParam(value = "enum_query_integer", required = false) Integer enumQueryInteger,@ApiParam(value = "Query parameter enum test (double)" , allowableValues="NUMBER_1_DOT_1, NUMBER_MINUS_1_DOT_2") @RequestPart(value="enum_query_double", required=false)  Double enumQueryDouble);
+    ResponseEntity<Void> testEnumParameters(@ApiParam(value = "Form parameter enum test (string array)", allowableValues=">, $") @RequestPart(value="enum_form_string_array", required=false)  List<String> enumFormStringArray,@ApiParam(value = "Form parameter enum test (string)", allowableValues="_abc, -efg, (xyz)", defaultValue="-efg") @RequestPart(value="enum_form_string", required=false)  String enumFormString, @ApiParam(value = "Query parameter enum test (string array)", allowableValues = ">, $") @RequestParam(value = "enum_query_string_array", required = false) List<String> enumQueryStringArray, @ApiParam(value = "Query parameter enum test (string)", allowableValues = "_abc, -efg, (xyz)", defaultValue = "-efg") @RequestParam(value = "enum_query_string", required = false, defaultValue="-efg") String enumQueryString, @ApiParam(value = "Query parameter enum test (double)", allowableValues = "1, -2") @RequestParam(value = "enum_query_integer", required = false) Integer enumQueryInteger,@ApiParam(value = "Query parameter enum test (double)", allowableValues="1.1, -1.2") @RequestPart(value="enum_query_double", required=false)  Double enumQueryDouble);
 
 }
diff --git a/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/api/FakeApiController.java b/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/api/FakeApiController.java
index 33ebb6847d..c4d23c4420 100644
--- a/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/api/FakeApiController.java
+++ b/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/api/FakeApiController.java
@@ -31,30 +31,30 @@ public class FakeApiController implements FakeApi {
         return new ResponseEntity<Client>(HttpStatus.OK);
     }
 
-    public ResponseEntity<Void> testEndpointParameters(@ApiParam(value = "None", required=true ) @RequestPart(value="number", required=true)  BigDecimal number,
-        @ApiParam(value = "None", required=true ) @RequestPart(value="double", required=true)  Double _double,
-        @ApiParam(value = "None", required=true ) @RequestPart(value="pattern_without_delimiter", required=true)  String patternWithoutDelimiter,
-        @ApiParam(value = "None", required=true ) @RequestPart(value="byte", required=true)  byte[] _byte,
-        @ApiParam(value = "None" ) @RequestPart(value="integer", required=false)  Integer integer,
-        @ApiParam(value = "None" ) @RequestPart(value="int32", required=false)  Integer int32,
-        @ApiParam(value = "None" ) @RequestPart(value="int64", required=false)  Long int64,
-        @ApiParam(value = "None" ) @RequestPart(value="float", required=false)  Float _float,
-        @ApiParam(value = "None" ) @RequestPart(value="string", required=false)  String string,
-        @ApiParam(value = "None" ) @RequestPart(value="binary", required=false)  byte[] binary,
-        @ApiParam(value = "None" ) @RequestPart(value="date", required=false)  LocalDate date,
-        @ApiParam(value = "None" ) @RequestPart(value="dateTime", required=false)  DateTime dateTime,
-        @ApiParam(value = "None" ) @RequestPart(value="password", required=false)  String password,
-        @ApiParam(value = "None" ) @RequestPart(value="callback", required=false)  String paramCallback) {
+    public ResponseEntity<Void> testEndpointParameters(@ApiParam(value = "None", required=true) @RequestPart(value="number", required=true)  BigDecimal number,
+        @ApiParam(value = "None", required=true) @RequestPart(value="double", required=true)  Double _double,
+        @ApiParam(value = "None", required=true) @RequestPart(value="pattern_without_delimiter", required=true)  String patternWithoutDelimiter,
+        @ApiParam(value = "None", required=true) @RequestPart(value="byte", required=true)  byte[] _byte,
+        @ApiParam(value = "None") @RequestPart(value="integer", required=false)  Integer integer,
+        @ApiParam(value = "None") @RequestPart(value="int32", required=false)  Integer int32,
+        @ApiParam(value = "None") @RequestPart(value="int64", required=false)  Long int64,
+        @ApiParam(value = "None") @RequestPart(value="float", required=false)  Float _float,
+        @ApiParam(value = "None") @RequestPart(value="string", required=false)  String string,
+        @ApiParam(value = "None") @RequestPart(value="binary", required=false)  byte[] binary,
+        @ApiParam(value = "None") @RequestPart(value="date", required=false)  LocalDate date,
+        @ApiParam(value = "None") @RequestPart(value="dateTime", required=false)  DateTime dateTime,
+        @ApiParam(value = "None") @RequestPart(value="password", required=false)  String password,
+        @ApiParam(value = "None") @RequestPart(value="callback", required=false)  String paramCallback) {
         // do some magic!
         return new ResponseEntity<Void>(HttpStatus.OK);
     }
 
-    public ResponseEntity<Void> testEnumParameters(@ApiParam(value = "Form parameter enum test (string array)" , allowableValues="GREATER_THAN, DOLLAR") @RequestPart(value="enum_form_string_array", required=false)  List<String> enumFormStringArray,
-        @ApiParam(value = "Form parameter enum test (string)" , allowableValues="_ABC, _EFG, _XYZ_", defaultValue="-efg") @RequestPart(value="enum_form_string", required=false)  String enumFormString,
-         @ApiParam(value = "Query parameter enum test (string array)", allowableValues = "GREATER_THAN, DOLLAR") @RequestParam(value = "enum_query_string_array", required = false) List<String> enumQueryStringArray,
-         @ApiParam(value = "Query parameter enum test (string)", allowableValues = "_ABC, _EFG, _XYZ_", defaultValue = "-efg") @RequestParam(value = "enum_query_string", required = false, defaultValue="-efg") String enumQueryString,
-         @ApiParam(value = "Query parameter enum test (double)", allowableValues = "NUMBER_1, NUMBER_MINUS_2") @RequestParam(value = "enum_query_integer", required = false) Integer enumQueryInteger,
-        @ApiParam(value = "Query parameter enum test (double)" , allowableValues="NUMBER_1_DOT_1, NUMBER_MINUS_1_DOT_2") @RequestPart(value="enum_query_double", required=false)  Double enumQueryDouble) {
+    public ResponseEntity<Void> testEnumParameters(@ApiParam(value = "Form parameter enum test (string array)", allowableValues=">, $") @RequestPart(value="enum_form_string_array", required=false)  List<String> enumFormStringArray,
+        @ApiParam(value = "Form parameter enum test (string)", allowableValues="_abc, -efg, (xyz)", defaultValue="-efg") @RequestPart(value="enum_form_string", required=false)  String enumFormString,
+         @ApiParam(value = "Query parameter enum test (string array)", allowableValues = ">, $") @RequestParam(value = "enum_query_string_array", required = false) List<String> enumQueryStringArray,
+         @ApiParam(value = "Query parameter enum test (string)", allowableValues = "_abc, -efg, (xyz)", defaultValue = "-efg") @RequestParam(value = "enum_query_string", required = false, defaultValue="-efg") String enumQueryString,
+         @ApiParam(value = "Query parameter enum test (double)", allowableValues = "1, -2") @RequestParam(value = "enum_query_integer", required = false) Integer enumQueryInteger,
+        @ApiParam(value = "Query parameter enum test (double)", allowableValues="1.1, -1.2") @RequestPart(value="enum_query_double", required=false)  Double enumQueryDouble) {
         // do some magic!
         return new ResponseEntity<Void>(HttpStatus.OK);
     }
diff --git a/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/api/PetApi.java b/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/api/PetApi.java
index deb708121c..3c7e400b4a 100644
--- a/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/api/PetApi.java
+++ b/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/api/PetApi.java
@@ -71,7 +71,7 @@ public interface PetApi {
     @RequestMapping(value = "/pet/findByStatus",
         produces = { "application/xml", "application/json" }, 
         method = RequestMethod.GET)
-    ResponseEntity<List<Pet>> findPetsByStatus( @NotNull @ApiParam(value = "Status values that need to be considered for filter", required = true, allowableValues = "AVAILABLE, PENDING, SOLD") @RequestParam(value = "status", required = true) List<String> status);
+    ResponseEntity<List<Pet>> findPetsByStatus( @NotNull @ApiParam(value = "Status values that need to be considered for filter", required = true, allowableValues = "available, pending, sold") @RequestParam(value = "status", required = true) List<String> status);
 
 
     @ApiOperation(value = "Finds Pets by tags", notes = "Multiple tags can be provided with comma separated strings. Use tag1, tag2, tag3 for testing.", response = Pet.class, responseContainer = "List", authorizations = {
@@ -143,7 +143,7 @@ public interface PetApi {
         produces = { "application/xml", "application/json" }, 
         consumes = { "application/x-www-form-urlencoded" },
         method = RequestMethod.POST)
-    ResponseEntity<Void> updatePetWithForm(@ApiParam(value = "ID of pet that needs to be updated",required=true ) @PathVariable("petId") Long petId,@ApiParam(value = "Updated name of the pet" ) @RequestPart(value="name", required=false)  String name,@ApiParam(value = "Updated status of the pet" ) @RequestPart(value="status", required=false)  String status);
+    ResponseEntity<Void> updatePetWithForm(@ApiParam(value = "ID of pet that needs to be updated",required=true ) @PathVariable("petId") Long petId,@ApiParam(value = "Updated name of the pet") @RequestPart(value="name", required=false)  String name,@ApiParam(value = "Updated status of the pet") @RequestPart(value="status", required=false)  String status);
 
 
     @ApiOperation(value = "uploads an image", notes = "", response = ModelApiResponse.class, authorizations = {
@@ -161,6 +161,6 @@ public interface PetApi {
         produces = { "application/json" }, 
         consumes = { "multipart/form-data" },
         method = RequestMethod.POST)
-    ResponseEntity<ModelApiResponse> uploadFile(@ApiParam(value = "ID of pet to update",required=true ) @PathVariable("petId") Long petId,@ApiParam(value = "Additional data to pass to server" ) @RequestPart(value="additionalMetadata", required=false)  String additionalMetadata,@ApiParam(value = "file detail") @RequestPart("file") MultipartFile file);
+    ResponseEntity<ModelApiResponse> uploadFile(@ApiParam(value = "ID of pet to update",required=true ) @PathVariable("petId") Long petId,@ApiParam(value = "Additional data to pass to server") @RequestPart(value="additionalMetadata", required=false)  String additionalMetadata,@ApiParam(value = "file detail") @RequestPart("file") MultipartFile file);
 
 }
diff --git a/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/api/PetApiController.java b/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/api/PetApiController.java
index b7c01ba2f0..1cd8ee75e4 100644
--- a/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/api/PetApiController.java
+++ b/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/api/PetApiController.java
@@ -35,7 +35,7 @@ public class PetApiController implements PetApi {
         return new ResponseEntity<Void>(HttpStatus.OK);
     }
 
-    public ResponseEntity<List<Pet>> findPetsByStatus( @NotNull @ApiParam(value = "Status values that need to be considered for filter", required = true, allowableValues = "AVAILABLE, PENDING, SOLD") @RequestParam(value = "status", required = true) List<String> status) {
+    public ResponseEntity<List<Pet>> findPetsByStatus( @NotNull @ApiParam(value = "Status values that need to be considered for filter", required = true, allowableValues = "available, pending, sold") @RequestParam(value = "status", required = true) List<String> status) {
         // do some magic!
         return new ResponseEntity<List<Pet>>(HttpStatus.OK);
     }
@@ -56,14 +56,14 @@ public class PetApiController implements PetApi {
     }
 
     public ResponseEntity<Void> updatePetWithForm(@ApiParam(value = "ID of pet that needs to be updated",required=true ) @PathVariable("petId") Long petId,
-        @ApiParam(value = "Updated name of the pet" ) @RequestPart(value="name", required=false)  String name,
-        @ApiParam(value = "Updated status of the pet" ) @RequestPart(value="status", required=false)  String status) {
+        @ApiParam(value = "Updated name of the pet") @RequestPart(value="name", required=false)  String name,
+        @ApiParam(value = "Updated status of the pet") @RequestPart(value="status", required=false)  String status) {
         // do some magic!
         return new ResponseEntity<Void>(HttpStatus.OK);
     }
 
     public ResponseEntity<ModelApiResponse> uploadFile(@ApiParam(value = "ID of pet to update",required=true ) @PathVariable("petId") Long petId,
-        @ApiParam(value = "Additional data to pass to server" ) @RequestPart(value="additionalMetadata", required=false)  String additionalMetadata,
+        @ApiParam(value = "Additional data to pass to server") @RequestPart(value="additionalMetadata", required=false)  String additionalMetadata,
         @ApiParam(value = "file detail") @RequestPart("file") MultipartFile file) {
         // do some magic!
         return new ResponseEntity<ModelApiResponse>(HttpStatus.OK);
diff --git a/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/model/AdditionalPropertiesClass.java b/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/model/AdditionalPropertiesClass.java
index 81535e041f..f4cfcadae5 100644
--- a/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/model/AdditionalPropertiesClass.java
+++ b/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/model/AdditionalPropertiesClass.java
@@ -15,10 +15,10 @@ import javax.validation.constraints.*;
 
 public class AdditionalPropertiesClass   {
   @JsonProperty("map_property")
-  private Map<String, String> mapProperty = new HashMap<String, String>();
+  private Map<String, String> mapProperty = null;
 
   @JsonProperty("map_of_map_property")
-  private Map<String, Map<String, String>> mapOfMapProperty = new HashMap<String, Map<String, String>>();
+  private Map<String, Map<String, String>> mapOfMapProperty = null;
 
   public AdditionalPropertiesClass mapProperty(Map<String, String> mapProperty) {
     this.mapProperty = mapProperty;
@@ -26,6 +26,9 @@ public class AdditionalPropertiesClass   {
   }
 
   public AdditionalPropertiesClass putMapPropertyItem(String key, String mapPropertyItem) {
+    if (this.mapProperty == null) {
+      this.mapProperty = new HashMap<String, String>();
+    }
     this.mapProperty.put(key, mapPropertyItem);
     return this;
   }
@@ -49,6 +52,9 @@ public class AdditionalPropertiesClass   {
   }
 
   public AdditionalPropertiesClass putMapOfMapPropertyItem(String key, Map<String, String> mapOfMapPropertyItem) {
+    if (this.mapOfMapProperty == null) {
+      this.mapOfMapProperty = new HashMap<String, Map<String, String>>();
+    }
     this.mapOfMapProperty.put(key, mapOfMapPropertyItem);
     return this;
   }
diff --git a/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/model/ArrayOfArrayOfNumberOnly.java b/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/model/ArrayOfArrayOfNumberOnly.java
index 3be691e4d9..8f975d8fed 100644
--- a/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/model/ArrayOfArrayOfNumberOnly.java
@@ -15,7 +15,7 @@ import javax.validation.constraints.*;
 
 public class ArrayOfArrayOfNumberOnly   {
   @JsonProperty("ArrayArrayNumber")
-  private List<List<BigDecimal>> arrayArrayNumber = new ArrayList<List<BigDecimal>>();
+  private List<List<BigDecimal>> arrayArrayNumber = null;
 
   public ArrayOfArrayOfNumberOnly arrayArrayNumber(List<List<BigDecimal>> arrayArrayNumber) {
     this.arrayArrayNumber = arrayArrayNumber;
@@ -23,6 +23,9 @@ public class ArrayOfArrayOfNumberOnly   {
   }
 
   public ArrayOfArrayOfNumberOnly addArrayArrayNumberItem(List<BigDecimal> arrayArrayNumberItem) {
+    if (this.arrayArrayNumber == null) {
+      this.arrayArrayNumber = new ArrayList<List<BigDecimal>>();
+    }
     this.arrayArrayNumber.add(arrayArrayNumberItem);
     return this;
   }
diff --git a/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/model/ArrayOfNumberOnly.java b/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/model/ArrayOfNumberOnly.java
index 1219689734..2c55600855 100644
--- a/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/model/ArrayOfNumberOnly.java
+++ b/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/model/ArrayOfNumberOnly.java
@@ -15,7 +15,7 @@ import javax.validation.constraints.*;
 
 public class ArrayOfNumberOnly   {
   @JsonProperty("ArrayNumber")
-  private List<BigDecimal> arrayNumber = new ArrayList<BigDecimal>();
+  private List<BigDecimal> arrayNumber = null;
 
   public ArrayOfNumberOnly arrayNumber(List<BigDecimal> arrayNumber) {
     this.arrayNumber = arrayNumber;
@@ -23,6 +23,9 @@ public class ArrayOfNumberOnly   {
   }
 
   public ArrayOfNumberOnly addArrayNumberItem(BigDecimal arrayNumberItem) {
+    if (this.arrayNumber == null) {
+      this.arrayNumber = new ArrayList<BigDecimal>();
+    }
     this.arrayNumber.add(arrayNumberItem);
     return this;
   }
diff --git a/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/model/ArrayTest.java b/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/model/ArrayTest.java
index a26a160028..664e319cd3 100644
--- a/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/model/ArrayTest.java
+++ b/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/model/ArrayTest.java
@@ -15,13 +15,13 @@ import javax.validation.constraints.*;
 
 public class ArrayTest   {
   @JsonProperty("array_of_string")
-  private List<String> arrayOfString = new ArrayList<String>();
+  private List<String> arrayOfString = null;
 
   @JsonProperty("array_array_of_integer")
-  private List<List<Long>> arrayArrayOfInteger = new ArrayList<List<Long>>();
+  private List<List<Long>> arrayArrayOfInteger = null;
 
   @JsonProperty("array_array_of_model")
-  private List<List<ReadOnlyFirst>> arrayArrayOfModel = new ArrayList<List<ReadOnlyFirst>>();
+  private List<List<ReadOnlyFirst>> arrayArrayOfModel = null;
 
   public ArrayTest arrayOfString(List<String> arrayOfString) {
     this.arrayOfString = arrayOfString;
@@ -29,6 +29,9 @@ public class ArrayTest   {
   }
 
   public ArrayTest addArrayOfStringItem(String arrayOfStringItem) {
+    if (this.arrayOfString == null) {
+      this.arrayOfString = new ArrayList<String>();
+    }
     this.arrayOfString.add(arrayOfStringItem);
     return this;
   }
@@ -52,6 +55,9 @@ public class ArrayTest   {
   }
 
   public ArrayTest addArrayArrayOfIntegerItem(List<Long> arrayArrayOfIntegerItem) {
+    if (this.arrayArrayOfInteger == null) {
+      this.arrayArrayOfInteger = new ArrayList<List<Long>>();
+    }
     this.arrayArrayOfInteger.add(arrayArrayOfIntegerItem);
     return this;
   }
@@ -75,6 +81,9 @@ public class ArrayTest   {
   }
 
   public ArrayTest addArrayArrayOfModelItem(List<ReadOnlyFirst> arrayArrayOfModelItem) {
+    if (this.arrayArrayOfModel == null) {
+      this.arrayArrayOfModel = new ArrayList<List<ReadOnlyFirst>>();
+    }
     this.arrayArrayOfModel.add(arrayArrayOfModelItem);
     return this;
   }
diff --git a/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/model/EnumArrays.java b/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/model/EnumArrays.java
index 97ab6f6410..f904035e48 100644
--- a/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/model/EnumArrays.java
+++ b/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/model/EnumArrays.java
@@ -80,7 +80,7 @@ public class EnumArrays   {
   }
 
   @JsonProperty("array_enum")
-  private List<ArrayEnumEnum> arrayEnum = new ArrayList<ArrayEnumEnum>();
+  private List<ArrayEnumEnum> arrayEnum = null;
 
   public EnumArrays justSymbol(JustSymbolEnum justSymbol) {
     this.justSymbol = justSymbol;
@@ -106,6 +106,9 @@ public class EnumArrays   {
   }
 
   public EnumArrays addArrayEnumItem(ArrayEnumEnum arrayEnumItem) {
+    if (this.arrayEnum == null) {
+      this.arrayEnum = new ArrayList<ArrayEnumEnum>();
+    }
     this.arrayEnum.add(arrayEnumItem);
     return this;
   }
diff --git a/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/model/MapTest.java b/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/model/MapTest.java
index 9a0566a8dd..434c3a8f1b 100644
--- a/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/model/MapTest.java
+++ b/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/model/MapTest.java
@@ -16,7 +16,7 @@ import javax.validation.constraints.*;
 
 public class MapTest   {
   @JsonProperty("map_map_of_string")
-  private Map<String, Map<String, String>> mapMapOfString = new HashMap<String, Map<String, String>>();
+  private Map<String, Map<String, String>> mapMapOfString = null;
 
   /**
    * Gets or Sets inner
@@ -50,7 +50,7 @@ public class MapTest   {
   }
 
   @JsonProperty("map_of_enum_string")
-  private Map<String, InnerEnum> mapOfEnumString = new HashMap<String, InnerEnum>();
+  private Map<String, InnerEnum> mapOfEnumString = null;
 
   public MapTest mapMapOfString(Map<String, Map<String, String>> mapMapOfString) {
     this.mapMapOfString = mapMapOfString;
@@ -58,6 +58,9 @@ public class MapTest   {
   }
 
   public MapTest putMapMapOfStringItem(String key, Map<String, String> mapMapOfStringItem) {
+    if (this.mapMapOfString == null) {
+      this.mapMapOfString = new HashMap<String, Map<String, String>>();
+    }
     this.mapMapOfString.put(key, mapMapOfStringItem);
     return this;
   }
@@ -81,6 +84,9 @@ public class MapTest   {
   }
 
   public MapTest putMapOfEnumStringItem(String key, InnerEnum mapOfEnumStringItem) {
+    if (this.mapOfEnumString == null) {
+      this.mapOfEnumString = new HashMap<String, InnerEnum>();
+    }
     this.mapOfEnumString.put(key, mapOfEnumStringItem);
     return this;
   }
diff --git a/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/model/MixedPropertiesAndAdditionalPropertiesClass.java b/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/model/MixedPropertiesAndAdditionalPropertiesClass.java
index 2cb9928d5f..dba1241f6d 100644
--- a/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/model/MixedPropertiesAndAdditionalPropertiesClass.java
+++ b/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/model/MixedPropertiesAndAdditionalPropertiesClass.java
@@ -24,7 +24,7 @@ public class MixedPropertiesAndAdditionalPropertiesClass   {
   private DateTime dateTime = null;
 
   @JsonProperty("map")
-  private Map<String, Animal> map = new HashMap<String, Animal>();
+  private Map<String, Animal> map = null;
 
   public MixedPropertiesAndAdditionalPropertiesClass uuid(UUID uuid) {
     this.uuid = uuid;
@@ -68,6 +68,9 @@ public class MixedPropertiesAndAdditionalPropertiesClass   {
   }
 
   public MixedPropertiesAndAdditionalPropertiesClass putMapItem(String key, Animal mapItem) {
+    if (this.map == null) {
+      this.map = new HashMap<String, Animal>();
+    }
     this.map.put(key, mapItem);
     return this;
   }
diff --git a/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/model/Pet.java b/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/model/Pet.java
index 9adc708de7..b013846b4d 100644
--- a/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/model/Pet.java
+++ b/samples/server/petstore/springboot-implicitHeaders/src/main/java/io/swagger/model/Pet.java
@@ -29,7 +29,7 @@ public class Pet   {
   private List<String> photoUrls = new ArrayList<String>();
 
   @JsonProperty("tags")
-  private List<Tag> tags = new ArrayList<Tag>();
+  private List<Tag> tags = null;
 
   /**
    * pet status in the store
@@ -152,6 +152,9 @@ public class Pet   {
   }
 
   public Pet addTagsItem(Tag tagsItem) {
+    if (this.tags == null) {
+      this.tags = new ArrayList<Tag>();
+    }
     this.tags.add(tagsItem);
     return this;
   }
diff --git a/samples/server/petstore/springboot/src/main/java/io/swagger/model/AdditionalPropertiesClass.java b/samples/server/petstore/springboot/src/main/java/io/swagger/model/AdditionalPropertiesClass.java
index d05e148df5..f4cfcadae5 100644
--- a/samples/server/petstore/springboot/src/main/java/io/swagger/model/AdditionalPropertiesClass.java
+++ b/samples/server/petstore/springboot/src/main/java/io/swagger/model/AdditionalPropertiesClass.java
@@ -26,6 +26,9 @@ public class AdditionalPropertiesClass   {
   }
 
   public AdditionalPropertiesClass putMapPropertyItem(String key, String mapPropertyItem) {
+    if (this.mapProperty == null) {
+      this.mapProperty = new HashMap<String, String>();
+    }
     this.mapProperty.put(key, mapPropertyItem);
     return this;
   }
@@ -49,6 +52,9 @@ public class AdditionalPropertiesClass   {
   }
 
   public AdditionalPropertiesClass putMapOfMapPropertyItem(String key, Map<String, String> mapOfMapPropertyItem) {
+    if (this.mapOfMapProperty == null) {
+      this.mapOfMapProperty = new HashMap<String, Map<String, String>>();
+    }
     this.mapOfMapProperty.put(key, mapOfMapPropertyItem);
     return this;
   }
diff --git a/samples/server/petstore/springboot/src/main/java/io/swagger/model/ArrayOfArrayOfNumberOnly.java b/samples/server/petstore/springboot/src/main/java/io/swagger/model/ArrayOfArrayOfNumberOnly.java
index f60805cc02..8f975d8fed 100644
--- a/samples/server/petstore/springboot/src/main/java/io/swagger/model/ArrayOfArrayOfNumberOnly.java
+++ b/samples/server/petstore/springboot/src/main/java/io/swagger/model/ArrayOfArrayOfNumberOnly.java
@@ -23,6 +23,9 @@ public class ArrayOfArrayOfNumberOnly   {
   }
 
   public ArrayOfArrayOfNumberOnly addArrayArrayNumberItem(List<BigDecimal> arrayArrayNumberItem) {
+    if (this.arrayArrayNumber == null) {
+      this.arrayArrayNumber = new ArrayList<List<BigDecimal>>();
+    }
     this.arrayArrayNumber.add(arrayArrayNumberItem);
     return this;
   }
diff --git a/samples/server/petstore/springboot/src/main/java/io/swagger/model/ArrayOfNumberOnly.java b/samples/server/petstore/springboot/src/main/java/io/swagger/model/ArrayOfNumberOnly.java
index d4f0f5010e..2c55600855 100644
--- a/samples/server/petstore/springboot/src/main/java/io/swagger/model/ArrayOfNumberOnly.java
+++ b/samples/server/petstore/springboot/src/main/java/io/swagger/model/ArrayOfNumberOnly.java
@@ -23,6 +23,9 @@ public class ArrayOfNumberOnly   {
   }
 
   public ArrayOfNumberOnly addArrayNumberItem(BigDecimal arrayNumberItem) {
+    if (this.arrayNumber == null) {
+      this.arrayNumber = new ArrayList<BigDecimal>();
+    }
     this.arrayNumber.add(arrayNumberItem);
     return this;
   }
diff --git a/samples/server/petstore/springboot/src/main/java/io/swagger/model/ArrayTest.java b/samples/server/petstore/springboot/src/main/java/io/swagger/model/ArrayTest.java
index 10c4c6c646..664e319cd3 100644
--- a/samples/server/petstore/springboot/src/main/java/io/swagger/model/ArrayTest.java
+++ b/samples/server/petstore/springboot/src/main/java/io/swagger/model/ArrayTest.java
@@ -29,6 +29,9 @@ public class ArrayTest   {
   }
 
   public ArrayTest addArrayOfStringItem(String arrayOfStringItem) {
+    if (this.arrayOfString == null) {
+      this.arrayOfString = new ArrayList<String>();
+    }
     this.arrayOfString.add(arrayOfStringItem);
     return this;
   }
@@ -52,6 +55,9 @@ public class ArrayTest   {
   }
 
   public ArrayTest addArrayArrayOfIntegerItem(List<Long> arrayArrayOfIntegerItem) {
+    if (this.arrayArrayOfInteger == null) {
+      this.arrayArrayOfInteger = new ArrayList<List<Long>>();
+    }
     this.arrayArrayOfInteger.add(arrayArrayOfIntegerItem);
     return this;
   }
@@ -75,6 +81,9 @@ public class ArrayTest   {
   }
 
   public ArrayTest addArrayArrayOfModelItem(List<ReadOnlyFirst> arrayArrayOfModelItem) {
+    if (this.arrayArrayOfModel == null) {
+      this.arrayArrayOfModel = new ArrayList<List<ReadOnlyFirst>>();
+    }
     this.arrayArrayOfModel.add(arrayArrayOfModelItem);
     return this;
   }
diff --git a/samples/server/petstore/springboot/src/main/java/io/swagger/model/EnumArrays.java b/samples/server/petstore/springboot/src/main/java/io/swagger/model/EnumArrays.java
index 06bb785ce0..f904035e48 100644
--- a/samples/server/petstore/springboot/src/main/java/io/swagger/model/EnumArrays.java
+++ b/samples/server/petstore/springboot/src/main/java/io/swagger/model/EnumArrays.java
@@ -106,6 +106,9 @@ public class EnumArrays   {
   }
 
   public EnumArrays addArrayEnumItem(ArrayEnumEnum arrayEnumItem) {
+    if (this.arrayEnum == null) {
+      this.arrayEnum = new ArrayList<ArrayEnumEnum>();
+    }
     this.arrayEnum.add(arrayEnumItem);
     return this;
   }
diff --git a/samples/server/petstore/springboot/src/main/java/io/swagger/model/MapTest.java b/samples/server/petstore/springboot/src/main/java/io/swagger/model/MapTest.java
index 9b6fc7acef..434c3a8f1b 100644
--- a/samples/server/petstore/springboot/src/main/java/io/swagger/model/MapTest.java
+++ b/samples/server/petstore/springboot/src/main/java/io/swagger/model/MapTest.java
@@ -58,6 +58,9 @@ public class MapTest   {
   }
 
   public MapTest putMapMapOfStringItem(String key, Map<String, String> mapMapOfStringItem) {
+    if (this.mapMapOfString == null) {
+      this.mapMapOfString = new HashMap<String, Map<String, String>>();
+    }
     this.mapMapOfString.put(key, mapMapOfStringItem);
     return this;
   }
@@ -81,6 +84,9 @@ public class MapTest   {
   }
 
   public MapTest putMapOfEnumStringItem(String key, InnerEnum mapOfEnumStringItem) {
+    if (this.mapOfEnumString == null) {
+      this.mapOfEnumString = new HashMap<String, InnerEnum>();
+    }
     this.mapOfEnumString.put(key, mapOfEnumStringItem);
     return this;
   }
diff --git a/samples/server/petstore/springboot/src/main/java/io/swagger/model/MixedPropertiesAndAdditionalPropertiesClass.java b/samples/server/petstore/springboot/src/main/java/io/swagger/model/MixedPropertiesAndAdditionalPropertiesClass.java
index 66e8b53b9b..dba1241f6d 100644
--- a/samples/server/petstore/springboot/src/main/java/io/swagger/model/MixedPropertiesAndAdditionalPropertiesClass.java
+++ b/samples/server/petstore/springboot/src/main/java/io/swagger/model/MixedPropertiesAndAdditionalPropertiesClass.java
@@ -68,6 +68,9 @@ public class MixedPropertiesAndAdditionalPropertiesClass   {
   }
 
   public MixedPropertiesAndAdditionalPropertiesClass putMapItem(String key, Animal mapItem) {
+    if (this.map == null) {
+      this.map = new HashMap<String, Animal>();
+    }
     this.map.put(key, mapItem);
     return this;
   }
diff --git a/samples/server/petstore/springboot/src/main/java/io/swagger/model/Pet.java b/samples/server/petstore/springboot/src/main/java/io/swagger/model/Pet.java
index 566cbc43a6..b013846b4d 100644
--- a/samples/server/petstore/springboot/src/main/java/io/swagger/model/Pet.java
+++ b/samples/server/petstore/springboot/src/main/java/io/swagger/model/Pet.java
@@ -152,6 +152,9 @@ public class Pet   {
   }
 
   public Pet addTagsItem(Tag tagsItem) {
+    if (this.tags == null) {
+      this.tags = new ArrayList<Tag>();
+    }
     this.tags.add(tagsItem);
     return this;
   }