fixed builder, error msg

modules/swagger-codegen/src/main/resources/Java/apiInvoker.mustache

@@ -226,7 +226,7 @@ public class ApiInvoker {
     }
     else if ("DELETE".equals(method)) {
       if(body == null)
-        response = builder.delete(ClientResponse.class, serialize(body));
+        response = builder.delete(ClientResponse.class);
       else
         response = builder.type(contentType).delete(ClientResponse.class, serialize(body));
     }
@@ -237,12 +237,26 @@ public class ApiInvoker {
       return null;
     }
     else if(response.getClientResponseStatus().getFamily() == Family.SUCCESSFUL) {
-      return (String) response.getEntity(String.class);
+      if(response.hasEntity()) {
+        return (String) response.getEntity(String.class);
+      }
+      else {
+        return "";
+      }
     }
     else {
+      String message = "error";
+      if(response.hasEntity()) {
+        try{
+          message = String.valueOf(response.getEntity(String.class));
+        }
+        catch (RuntimeException e) {
+          // e.printStackTrace();
+        }
+      }
       throw new ApiException(
                 response.getClientResponseStatus().getStatusCode(),
-                response.getEntity(String.class));
+                message);
     }
   }