[BUG][Go] Remove "null" body value when body is empty #13927 (#13934)

* only write reponse body if not nil

* update go samples

* golang style convention

modules/openapi-generator/src/main/resources/go-server/routers.mustache

@@ -108,7 +108,11 @@ func EncodeJSONResponse(i interface{}, status *int,{{#addResponseHeaders}} heade
 		w.WriteHeader(http.StatusOK)
 	}
 
-	return json.NewEncoder(w).Encode(i)
+    if i != nil {
+        return json.NewEncoder(w).Encode(i)
+    }
+
+    return nil
 }
 
 // ReadFormFileToTempFile reads file data from a request form and writes it to a temporary file

samples/server/petstore/go-api-server/go/routers.go

@@ -76,7 +76,11 @@ func EncodeJSONResponse(i interface{}, status *int, headers map[string][]string,
 		w.WriteHeader(http.StatusOK)
 	}
 
-	return json.NewEncoder(w).Encode(i)
+    if i != nil {
+        return json.NewEncoder(w).Encode(i)
+    }
+
+    return nil
 }
 
 // ReadFormFileToTempFile reads file data from a request form and writes it to a temporary file

samples/server/petstore/go-chi-server/go/routers.go

@@ -72,7 +72,11 @@ func EncodeJSONResponse(i interface{}, status *int, headers map[string][]string,
 		w.WriteHeader(http.StatusOK)
 	}
 
-	return json.NewEncoder(w).Encode(i)
+    if i != nil {
+        return json.NewEncoder(w).Encode(i)
+    }
+
+    return nil
 }
 
 // ReadFormFileToTempFile reads file data from a request form and writes it to a temporary file

samples/server/petstore/go-server-required/go/routers.go

@@ -72,7 +72,11 @@ func EncodeJSONResponse(i interface{}, status *int, headers map[string][]string,
 		w.WriteHeader(http.StatusOK)
 	}
 
-	return json.NewEncoder(w).Encode(i)
+    if i != nil {
+        return json.NewEncoder(w).Encode(i)
+    }
+
+    return nil
 }
 
 // ReadFormFileToTempFile reads file data from a request form and writes it to a temporary file