diff --git a/modules/swagger-codegen/src/main/resources/Java/api.mustache b/modules/swagger-codegen/src/main/resources/Java/api.mustache
index 542ccbba287..383c310e579 100644
--- a/modules/swagger-codegen/src/main/resources/Java/api.mustache
+++ b/modules/swagger-codegen/src/main/resources/Java/api.mustache
@@ -64,7 +64,7 @@ public class {{classname}} {
   @Deprecated
   {{/isDeprecated}}
   public {{#returnType}}{{{returnType}}} {{/returnType}}{{^returnType}}void {{/returnType}}{{operationId}}({{#allParams}}{{{dataType}}} {{paramName}}{{#hasMore}}, {{/hasMore}}{{/allParams}}) throws ApiException {
-    Object {{localVariablePrefix}}localVarPostBody = {{#bodyParam}}{{paramName}}{{/bodyParam}}{{^bodyParam}}null{{/bodyParam}};
+    Object {{localVariablePrefix}}localVarPostBody = {{#bodyParam}}{{paramName}}{{/bodyParam}}{{^bodyParam}}new Object(){{/bodyParam}};
     {{#allParams}}{{#required}}
     // verify the required parameter '{{paramName}}' is set
     if ({{paramName}} == null) {
diff --git a/modules/swagger-codegen/src/main/resources/Java/libraries/jersey2/api.mustache b/modules/swagger-codegen/src/main/resources/Java/libraries/jersey2/api.mustache
index fed034609c8..17f27e94a3d 100644
--- a/modules/swagger-codegen/src/main/resources/Java/libraries/jersey2/api.mustache
+++ b/modules/swagger-codegen/src/main/resources/Java/libraries/jersey2/api.mustache
@@ -91,7 +91,7 @@ public class {{classname}} {
   @Deprecated
   {{/isDeprecated}}
   public ApiResponse<{{#returnType}}{{{returnType}}}{{/returnType}}{{^returnType}}Void{{/returnType}}> {{operationId}}WithHttpInfo({{#allParams}}{{{dataType}}} {{paramName}}{{#hasMore}}, {{/hasMore}}{{/allParams}}) throws ApiException {
-    Object {{localVariablePrefix}}localVarPostBody = {{#bodyParam}}{{paramName}}{{/bodyParam}}{{^bodyParam}}null{{/bodyParam}};
+    Object {{localVariablePrefix}}localVarPostBody = {{#bodyParam}}{{paramName}}{{/bodyParam}}{{^bodyParam}}new Object(){{/bodyParam}};
     {{#allParams}}{{#required}}
     // verify the required parameter '{{paramName}}' is set
     if ({{paramName}} == null) {
diff --git a/modules/swagger-codegen/src/main/resources/Java/libraries/okhttp-gson/api.mustache b/modules/swagger-codegen/src/main/resources/Java/libraries/okhttp-gson/api.mustache
index ffc68bc7b5a..f6ab4d05e45 100644
--- a/modules/swagger-codegen/src/main/resources/Java/libraries/okhttp-gson/api.mustache
+++ b/modules/swagger-codegen/src/main/resources/Java/libraries/okhttp-gson/api.mustache
@@ -82,7 +82,7 @@ public class {{classname}} {
     @Deprecated
     {{/isDeprecated}}
     public com.squareup.okhttp.Call {{operationId}}Call({{#allParams}}{{{dataType}}} {{paramName}}, {{/allParams}}final ProgressResponseBody.ProgressListener progressListener, final ProgressRequestBody.ProgressRequestListener progressRequestListener) throws ApiException {
-        Object {{localVariablePrefix}}localVarPostBody = {{#bodyParam}}{{paramName}}{{/bodyParam}}{{^bodyParam}}null{{/bodyParam}};
+        Object {{localVariablePrefix}}localVarPostBody = {{#bodyParam}}{{paramName}}{{/bodyParam}}{{^bodyParam}}new Object(){{/bodyParam}};
 
         // create path and map variables
         String {{localVariablePrefix}}localVarPath = "{{{path}}}"{{#pathParams}}
diff --git a/modules/swagger-codegen/src/main/resources/Java/libraries/resteasy/api.mustache b/modules/swagger-codegen/src/main/resources/Java/libraries/resteasy/api.mustache
index f3fd01ed61b..bd70d88a2dd 100644
--- a/modules/swagger-codegen/src/main/resources/Java/libraries/resteasy/api.mustache
+++ b/modules/swagger-codegen/src/main/resources/Java/libraries/resteasy/api.mustache
@@ -57,7 +57,7 @@ public class {{classname}} {
   @Deprecated
   {{/isDeprecated}}
   public {{#returnType}}{{{returnType}}} {{/returnType}}{{^returnType}}void {{/returnType}}{{operationId}}({{#allParams}}{{{dataType}}} {{paramName}}{{#hasMore}}, {{/hasMore}}{{/allParams}}) throws ApiException {
-    Object {{localVariablePrefix}}localVarPostBody = {{#bodyParam}}{{paramName}}{{/bodyParam}}{{^bodyParam}}null{{/bodyParam}};
+    Object {{localVariablePrefix}}localVarPostBody = {{#bodyParam}}{{paramName}}{{/bodyParam}}{{^bodyParam}}new Object(){{/bodyParam}};
     {{#allParams}}{{#required}}
     // verify the required parameter '{{paramName}}' is set
     if ({{paramName}} == null) {
diff --git a/modules/swagger-codegen/src/main/resources/Java/libraries/resttemplate/api.mustache b/modules/swagger-codegen/src/main/resources/Java/libraries/resttemplate/api.mustache
index f48180f4381..a906a80e7a8 100644
--- a/modules/swagger-codegen/src/main/resources/Java/libraries/resttemplate/api.mustache
+++ b/modules/swagger-codegen/src/main/resources/Java/libraries/resttemplate/api.mustache
@@ -61,7 +61,7 @@ public class {{classname}} {
 {{/externalDocs}}
      */
     public {{#returnType}}{{{returnType}}} {{/returnType}}{{^returnType}}void {{/returnType}}{{operationId}}({{#allParams}}{{{dataType}}} {{paramName}}{{#hasMore}}, {{/hasMore}}{{/allParams}}) throws RestClientException {
-        Object {{localVariablePrefix}}postBody = {{#bodyParam}}{{paramName}}{{/bodyParam}}{{^bodyParam}}null{{/bodyParam}};
+        Object {{localVariablePrefix}}postBody = {{#bodyParam}}{{paramName}}{{/bodyParam}}{{^bodyParam}}new Object(){{/bodyParam}};
         {{#allParams}}{{#required}}
         // verify the required parameter '{{paramName}}' is set
         if ({{paramName}} == null) {
diff --git a/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/api/FakeApi.java b/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/api/FakeApi.java
index 2e6a3b08728..27fd92085f2 100644
--- a/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/api/FakeApi.java
+++ b/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/api/FakeApi.java
@@ -311,7 +311,7 @@ public Client testClientModel(Client body) throws ApiException {
    * @throws ApiException if fails to make API call
    */
   public void testEndpointParameters(BigDecimal number, Double _double, String patternWithoutDelimiter, byte[] _byte, Integer integer, Integer int32, Long int64, Float _float, String string, byte[] binary, LocalDate date, OffsetDateTime dateTime, String password, String paramCallback) throws ApiException {
-    Object localVarPostBody = null;
+    Object localVarPostBody = new Object();
     
     // verify the required parameter 'number' is set
     if (number == null) {
@@ -402,7 +402,7 @@ public void testEndpointParameters(BigDecimal number, Double _double, String pat
    * @throws ApiException if fails to make API call
    */
   public void testEnumParameters(List<String> enumFormStringArray, String enumFormString, List<String> enumHeaderStringArray, String enumHeaderString, List<String> enumQueryStringArray, String enumQueryString, Integer enumQueryInteger, Double enumQueryDouble) throws ApiException {
-    Object localVarPostBody = null;
+    Object localVarPostBody = new Object();
     
     // create path and map variables
     String localVarPath = "/fake";
@@ -493,7 +493,7 @@ public void testInlineAdditionalProperties(Object param) throws ApiException {
    * @throws ApiException if fails to make API call
    */
   public void testJsonFormData(String param, String param2) throws ApiException {
-    Object localVarPostBody = null;
+    Object localVarPostBody = new Object();
     
     // verify the required parameter 'param' is set
     if (param == null) {
diff --git a/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/api/PetApi.java b/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/api/PetApi.java
index edd3fb24885..3184b3dace8 100644
--- a/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/api/PetApi.java
+++ b/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/api/PetApi.java
@@ -99,7 +99,7 @@ public void addPet(Pet body) throws ApiException {
    * @throws ApiException if fails to make API call
    */
   public void deletePet(Long petId, String apiKey) throws ApiException {
-    Object localVarPostBody = null;
+    Object localVarPostBody = new Object();
     
     // verify the required parameter 'petId' is set
     if (petId == null) {
@@ -144,7 +144,7 @@ public void deletePet(Long petId, String apiKey) throws ApiException {
    * @throws ApiException if fails to make API call
    */
   public List<Pet> findPetsByStatus(List<String> status) throws ApiException {
-    Object localVarPostBody = null;
+    Object localVarPostBody = new Object();
     
     // verify the required parameter 'status' is set
     if (status == null) {
@@ -189,7 +189,7 @@ public List<Pet> findPetsByStatus(List<String> status) throws ApiException {
    */
   @Deprecated
   public List<Pet> findPetsByTags(List<String> tags) throws ApiException {
-    Object localVarPostBody = null;
+    Object localVarPostBody = new Object();
     
     // verify the required parameter 'tags' is set
     if (tags == null) {
@@ -232,7 +232,7 @@ public List<Pet> findPetsByTags(List<String> tags) throws ApiException {
    * @throws ApiException if fails to make API call
    */
   public Pet getPetById(Long petId) throws ApiException {
-    Object localVarPostBody = null;
+    Object localVarPostBody = new Object();
     
     // verify the required parameter 'petId' is set
     if (petId == null) {
@@ -317,7 +317,7 @@ public void updatePet(Pet body) throws ApiException {
    * @throws ApiException if fails to make API call
    */
   public void updatePetWithForm(Long petId, String name, String status) throws ApiException {
-    Object localVarPostBody = null;
+    Object localVarPostBody = new Object();
     
     // verify the required parameter 'petId' is set
     if (petId == null) {
@@ -366,7 +366,7 @@ public void updatePetWithForm(Long petId, String name, String status) throws Api
    * @throws ApiException if fails to make API call
    */
   public ModelApiResponse uploadFile(Long petId, String additionalMetadata, File file) throws ApiException {
-    Object localVarPostBody = null;
+    Object localVarPostBody = new Object();
     
     // verify the required parameter 'petId' is set
     if (petId == null) {
diff --git a/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/api/StoreApi.java b/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/api/StoreApi.java
index 0c8a68f5d21..d316c9dc498 100644
--- a/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/api/StoreApi.java
+++ b/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/api/StoreApi.java
@@ -55,7 +55,7 @@ public void setApiClient(ApiClient apiClient) {
    * @throws ApiException if fails to make API call
    */
   public void deleteOrder(String orderId) throws ApiException {
-    Object localVarPostBody = null;
+    Object localVarPostBody = new Object();
     
     // verify the required parameter 'orderId' is set
     if (orderId == null) {
@@ -97,7 +97,7 @@ public void deleteOrder(String orderId) throws ApiException {
    * @throws ApiException if fails to make API call
    */
   public Map<String, Integer> getInventory() throws ApiException {
-    Object localVarPostBody = null;
+    Object localVarPostBody = new Object();
     
     // create path and map variables
     String localVarPath = "/store/inventory";
@@ -134,7 +134,7 @@ public Map<String, Integer> getInventory() throws ApiException {
    * @throws ApiException if fails to make API call
    */
   public Order getOrderById(Long orderId) throws ApiException {
-    Object localVarPostBody = null;
+    Object localVarPostBody = new Object();
     
     // verify the required parameter 'orderId' is set
     if (orderId == null) {
diff --git a/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/api/UserApi.java b/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/api/UserApi.java
index 5d44eb9cd82..2298fad6255 100644
--- a/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/api/UserApi.java
+++ b/samples/client/petstore/java/jersey1/src/main/java/io/swagger/client/api/UserApi.java
@@ -178,7 +178,7 @@ public void createUsersWithListInput(List<User> body) throws ApiException {
    * @throws ApiException if fails to make API call
    */
   public void deleteUser(String username) throws ApiException {
-    Object localVarPostBody = null;
+    Object localVarPostBody = new Object();
     
     // verify the required parameter 'username' is set
     if (username == null) {
@@ -221,7 +221,7 @@ public void deleteUser(String username) throws ApiException {
    * @throws ApiException if fails to make API call
    */
   public User getUserByName(String username) throws ApiException {
-    Object localVarPostBody = null;
+    Object localVarPostBody = new Object();
     
     // verify the required parameter 'username' is set
     if (username == null) {
@@ -265,7 +265,7 @@ public User getUserByName(String username) throws ApiException {
    * @throws ApiException if fails to make API call
    */
   public String loginUser(String username, String password) throws ApiException {
-    Object localVarPostBody = null;
+    Object localVarPostBody = new Object();
     
     // verify the required parameter 'username' is set
     if (username == null) {
@@ -312,7 +312,7 @@ public String loginUser(String username, String password) throws ApiException {
    * @throws ApiException if fails to make API call
    */
   public void logoutUser() throws ApiException {
-    Object localVarPostBody = null;
+    Object localVarPostBody = new Object();
     
     // create path and map variables
     String localVarPath = "/user/logout";
diff --git a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/api/FakeApi.java b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/api/FakeApi.java
index a442b24bd53..2876f4ea0ad 100644
--- a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/api/FakeApi.java
+++ b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/api/FakeApi.java
@@ -800,7 +800,7 @@ public void onRequestProgress(long bytesWritten, long contentLength, boolean don
      * @throws ApiException If fail to serialize the request body object
      */
     public com.squareup.okhttp.Call testEndpointParametersCall(BigDecimal number, Double _double, String patternWithoutDelimiter, byte[] _byte, Integer integer, Integer int32, Long int64, Float _float, String string, byte[] binary, LocalDate date, OffsetDateTime dateTime, String password, String paramCallback, final ProgressResponseBody.ProgressListener progressListener, final ProgressRequestBody.ProgressRequestListener progressRequestListener) throws ApiException {
-        Object localVarPostBody = null;
+        Object localVarPostBody = new Object();
 
         // create path and map variables
         String localVarPath = "/fake";
@@ -1007,7 +1007,7 @@ public void onRequestProgress(long bytesWritten, long contentLength, boolean don
      * @throws ApiException If fail to serialize the request body object
      */
     public com.squareup.okhttp.Call testEnumParametersCall(List<String> enumFormStringArray, String enumFormString, List<String> enumHeaderStringArray, String enumHeaderString, List<String> enumQueryStringArray, String enumQueryString, Integer enumQueryInteger, Double enumQueryDouble, final ProgressResponseBody.ProgressListener progressListener, final ProgressRequestBody.ProgressRequestListener progressRequestListener) throws ApiException {
-        Object localVarPostBody = null;
+        Object localVarPostBody = new Object();
 
         // create path and map variables
         String localVarPath = "/fake";
@@ -1276,7 +1276,7 @@ public void onRequestProgress(long bytesWritten, long contentLength, boolean don
      * @throws ApiException If fail to serialize the request body object
      */
     public com.squareup.okhttp.Call testJsonFormDataCall(String param, String param2, final ProgressResponseBody.ProgressListener progressListener, final ProgressRequestBody.ProgressRequestListener progressRequestListener) throws ApiException {
-        Object localVarPostBody = null;
+        Object localVarPostBody = new Object();
 
         // create path and map variables
         String localVarPath = "/fake/jsonFormData";
diff --git a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/api/PetApi.java b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/api/PetApi.java
index 23b9049e61b..163c787d854 100644
--- a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/api/PetApi.java
+++ b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/api/PetApi.java
@@ -184,7 +184,7 @@ public void onRequestProgress(long bytesWritten, long contentLength, boolean don
      * @throws ApiException If fail to serialize the request body object
      */
     public com.squareup.okhttp.Call deletePetCall(Long petId, String apiKey, final ProgressResponseBody.ProgressListener progressListener, final ProgressRequestBody.ProgressRequestListener progressRequestListener) throws ApiException {
-        Object localVarPostBody = null;
+        Object localVarPostBody = new Object();
 
         // create path and map variables
         String localVarPath = "/pet/{petId}"
@@ -308,7 +308,7 @@ public void onRequestProgress(long bytesWritten, long contentLength, boolean don
      * @throws ApiException If fail to serialize the request body object
      */
     public com.squareup.okhttp.Call findPetsByStatusCall(List<String> status, final ProgressResponseBody.ProgressListener progressListener, final ProgressRequestBody.ProgressRequestListener progressRequestListener) throws ApiException {
-        Object localVarPostBody = null;
+        Object localVarPostBody = new Object();
 
         // create path and map variables
         String localVarPath = "/pet/findByStatus";
@@ -434,7 +434,7 @@ public void onRequestProgress(long bytesWritten, long contentLength, boolean don
      */
     @Deprecated
     public com.squareup.okhttp.Call findPetsByTagsCall(List<String> tags, final ProgressResponseBody.ProgressListener progressListener, final ProgressRequestBody.ProgressRequestListener progressRequestListener) throws ApiException {
-        Object localVarPostBody = null;
+        Object localVarPostBody = new Object();
 
         // create path and map variables
         String localVarPath = "/pet/findByTags";
@@ -565,7 +565,7 @@ public void onRequestProgress(long bytesWritten, long contentLength, boolean don
      * @throws ApiException If fail to serialize the request body object
      */
     public com.squareup.okhttp.Call getPetByIdCall(Long petId, final ProgressResponseBody.ProgressListener progressListener, final ProgressRequestBody.ProgressRequestListener progressRequestListener) throws ApiException {
-        Object localVarPostBody = null;
+        Object localVarPostBody = new Object();
 
         // create path and map variables
         String localVarPath = "/pet/{petId}"
@@ -808,7 +808,7 @@ public void onRequestProgress(long bytesWritten, long contentLength, boolean don
      * @throws ApiException If fail to serialize the request body object
      */
     public com.squareup.okhttp.Call updatePetWithFormCall(Long petId, String name, String status, final ProgressResponseBody.ProgressListener progressListener, final ProgressRequestBody.ProgressRequestListener progressRequestListener) throws ApiException {
-        Object localVarPostBody = null;
+        Object localVarPostBody = new Object();
 
         // create path and map variables
         String localVarPath = "/pet/{petId}"
@@ -939,7 +939,7 @@ public void onRequestProgress(long bytesWritten, long contentLength, boolean don
      * @throws ApiException If fail to serialize the request body object
      */
     public com.squareup.okhttp.Call uploadFileCall(Long petId, String additionalMetadata, File file, final ProgressResponseBody.ProgressListener progressListener, final ProgressRequestBody.ProgressRequestListener progressRequestListener) throws ApiException {
-        Object localVarPostBody = null;
+        Object localVarPostBody = new Object();
 
         // create path and map variables
         String localVarPath = "/pet/{petId}/uploadImage"
diff --git a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/api/StoreApi.java b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/api/StoreApi.java
index a517a459d79..0bd2e2c1c62 100644
--- a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/api/StoreApi.java
+++ b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/api/StoreApi.java
@@ -63,7 +63,7 @@ public void setApiClient(ApiClient apiClient) {
      * @throws ApiException If fail to serialize the request body object
      */
     public com.squareup.okhttp.Call deleteOrderCall(String orderId, final ProgressResponseBody.ProgressListener progressListener, final ProgressRequestBody.ProgressRequestListener progressRequestListener) throws ApiException {
-        Object localVarPostBody = null;
+        Object localVarPostBody = new Object();
 
         // create path and map variables
         String localVarPath = "/store/order/{order_id}"
@@ -181,7 +181,7 @@ public void onRequestProgress(long bytesWritten, long contentLength, boolean don
      * @throws ApiException If fail to serialize the request body object
      */
     public com.squareup.okhttp.Call getInventoryCall(final ProgressResponseBody.ProgressListener progressListener, final ProgressRequestBody.ProgressRequestListener progressRequestListener) throws ApiException {
-        Object localVarPostBody = null;
+        Object localVarPostBody = new Object();
 
         // create path and map variables
         String localVarPath = "/store/inventory";
@@ -295,7 +295,7 @@ public void onRequestProgress(long bytesWritten, long contentLength, boolean don
      * @throws ApiException If fail to serialize the request body object
      */
     public com.squareup.okhttp.Call getOrderByIdCall(Long orderId, final ProgressResponseBody.ProgressListener progressListener, final ProgressRequestBody.ProgressRequestListener progressRequestListener) throws ApiException {
-        Object localVarPostBody = null;
+        Object localVarPostBody = new Object();
 
         // create path and map variables
         String localVarPath = "/store/order/{order_id}"
diff --git a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/api/UserApi.java b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/api/UserApi.java
index 518d851e31a..99532edeec8 100644
--- a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/api/UserApi.java
+++ b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/io/swagger/client/api/UserApi.java
@@ -417,7 +417,7 @@ public void onRequestProgress(long bytesWritten, long contentLength, boolean don
      * @throws ApiException If fail to serialize the request body object
      */
     public com.squareup.okhttp.Call deleteUserCall(String username, final ProgressResponseBody.ProgressListener progressListener, final ProgressRequestBody.ProgressRequestListener progressRequestListener) throws ApiException {
-        Object localVarPostBody = null;
+        Object localVarPostBody = new Object();
 
         // create path and map variables
         String localVarPath = "/user/{username}"
@@ -536,7 +536,7 @@ public void onRequestProgress(long bytesWritten, long contentLength, boolean don
      * @throws ApiException If fail to serialize the request body object
      */
     public com.squareup.okhttp.Call getUserByNameCall(String username, final ProgressResponseBody.ProgressListener progressListener, final ProgressRequestBody.ProgressRequestListener progressRequestListener) throws ApiException {
-        Object localVarPostBody = null;
+        Object localVarPostBody = new Object();
 
         // create path and map variables
         String localVarPath = "/user/{username}"
@@ -660,7 +660,7 @@ public void onRequestProgress(long bytesWritten, long contentLength, boolean don
      * @throws ApiException If fail to serialize the request body object
      */
     public com.squareup.okhttp.Call loginUserCall(String username, String password, final ProgressResponseBody.ProgressListener progressListener, final ProgressRequestBody.ProgressRequestListener progressRequestListener) throws ApiException {
-        Object localVarPostBody = null;
+        Object localVarPostBody = new Object();
 
         // create path and map variables
         String localVarPath = "/user/login";
@@ -793,7 +793,7 @@ public void onRequestProgress(long bytesWritten, long contentLength, boolean don
      * @throws ApiException If fail to serialize the request body object
      */
     public com.squareup.okhttp.Call logoutUserCall(final ProgressResponseBody.ProgressListener progressListener, final ProgressRequestBody.ProgressRequestListener progressRequestListener) throws ApiException {
-        Object localVarPostBody = null;
+        Object localVarPostBody = new Object();
 
         // create path and map variables
         String localVarPath = "/user/logout";
diff --git a/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/api/FakeApi.java b/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/api/FakeApi.java
index a442b24bd53..2876f4ea0ad 100644
--- a/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/api/FakeApi.java
+++ b/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/api/FakeApi.java
@@ -800,7 +800,7 @@ public void onRequestProgress(long bytesWritten, long contentLength, boolean don
      * @throws ApiException If fail to serialize the request body object
      */
     public com.squareup.okhttp.Call testEndpointParametersCall(BigDecimal number, Double _double, String patternWithoutDelimiter, byte[] _byte, Integer integer, Integer int32, Long int64, Float _float, String string, byte[] binary, LocalDate date, OffsetDateTime dateTime, String password, String paramCallback, final ProgressResponseBody.ProgressListener progressListener, final ProgressRequestBody.ProgressRequestListener progressRequestListener) throws ApiException {
-        Object localVarPostBody = null;
+        Object localVarPostBody = new Object();
 
         // create path and map variables
         String localVarPath = "/fake";
@@ -1007,7 +1007,7 @@ public void onRequestProgress(long bytesWritten, long contentLength, boolean don
      * @throws ApiException If fail to serialize the request body object
      */
     public com.squareup.okhttp.Call testEnumParametersCall(List<String> enumFormStringArray, String enumFormString, List<String> enumHeaderStringArray, String enumHeaderString, List<String> enumQueryStringArray, String enumQueryString, Integer enumQueryInteger, Double enumQueryDouble, final ProgressResponseBody.ProgressListener progressListener, final ProgressRequestBody.ProgressRequestListener progressRequestListener) throws ApiException {
-        Object localVarPostBody = null;
+        Object localVarPostBody = new Object();
 
         // create path and map variables
         String localVarPath = "/fake";
@@ -1276,7 +1276,7 @@ public void onRequestProgress(long bytesWritten, long contentLength, boolean don
      * @throws ApiException If fail to serialize the request body object
      */
     public com.squareup.okhttp.Call testJsonFormDataCall(String param, String param2, final ProgressResponseBody.ProgressListener progressListener, final ProgressRequestBody.ProgressRequestListener progressRequestListener) throws ApiException {
-        Object localVarPostBody = null;
+        Object localVarPostBody = new Object();
 
         // create path and map variables
         String localVarPath = "/fake/jsonFormData";
diff --git a/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/api/PetApi.java b/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/api/PetApi.java
index 23b9049e61b..163c787d854 100644
--- a/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/api/PetApi.java
+++ b/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/api/PetApi.java
@@ -184,7 +184,7 @@ public void onRequestProgress(long bytesWritten, long contentLength, boolean don
      * @throws ApiException If fail to serialize the request body object
      */
     public com.squareup.okhttp.Call deletePetCall(Long petId, String apiKey, final ProgressResponseBody.ProgressListener progressListener, final ProgressRequestBody.ProgressRequestListener progressRequestListener) throws ApiException {
-        Object localVarPostBody = null;
+        Object localVarPostBody = new Object();
 
         // create path and map variables
         String localVarPath = "/pet/{petId}"
@@ -308,7 +308,7 @@ public void onRequestProgress(long bytesWritten, long contentLength, boolean don
      * @throws ApiException If fail to serialize the request body object
      */
     public com.squareup.okhttp.Call findPetsByStatusCall(List<String> status, final ProgressResponseBody.ProgressListener progressListener, final ProgressRequestBody.ProgressRequestListener progressRequestListener) throws ApiException {
-        Object localVarPostBody = null;
+        Object localVarPostBody = new Object();
 
         // create path and map variables
         String localVarPath = "/pet/findByStatus";
@@ -434,7 +434,7 @@ public void onRequestProgress(long bytesWritten, long contentLength, boolean don
      */
     @Deprecated
     public com.squareup.okhttp.Call findPetsByTagsCall(List<String> tags, final ProgressResponseBody.ProgressListener progressListener, final ProgressRequestBody.ProgressRequestListener progressRequestListener) throws ApiException {
-        Object localVarPostBody = null;
+        Object localVarPostBody = new Object();
 
         // create path and map variables
         String localVarPath = "/pet/findByTags";
@@ -565,7 +565,7 @@ public void onRequestProgress(long bytesWritten, long contentLength, boolean don
      * @throws ApiException If fail to serialize the request body object
      */
     public com.squareup.okhttp.Call getPetByIdCall(Long petId, final ProgressResponseBody.ProgressListener progressListener, final ProgressRequestBody.ProgressRequestListener progressRequestListener) throws ApiException {
-        Object localVarPostBody = null;
+        Object localVarPostBody = new Object();
 
         // create path and map variables
         String localVarPath = "/pet/{petId}"
@@ -808,7 +808,7 @@ public void onRequestProgress(long bytesWritten, long contentLength, boolean don
      * @throws ApiException If fail to serialize the request body object
      */
     public com.squareup.okhttp.Call updatePetWithFormCall(Long petId, String name, String status, final ProgressResponseBody.ProgressListener progressListener, final ProgressRequestBody.ProgressRequestListener progressRequestListener) throws ApiException {
-        Object localVarPostBody = null;
+        Object localVarPostBody = new Object();
 
         // create path and map variables
         String localVarPath = "/pet/{petId}"
@@ -939,7 +939,7 @@ public void onRequestProgress(long bytesWritten, long contentLength, boolean don
      * @throws ApiException If fail to serialize the request body object
      */
     public com.squareup.okhttp.Call uploadFileCall(Long petId, String additionalMetadata, File file, final ProgressResponseBody.ProgressListener progressListener, final ProgressRequestBody.ProgressRequestListener progressRequestListener) throws ApiException {
-        Object localVarPostBody = null;
+        Object localVarPostBody = new Object();
 
         // create path and map variables
         String localVarPath = "/pet/{petId}/uploadImage"
diff --git a/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/api/StoreApi.java b/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/api/StoreApi.java
index a517a459d79..0bd2e2c1c62 100644
--- a/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/api/StoreApi.java
+++ b/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/api/StoreApi.java
@@ -63,7 +63,7 @@ public void setApiClient(ApiClient apiClient) {
      * @throws ApiException If fail to serialize the request body object
      */
     public com.squareup.okhttp.Call deleteOrderCall(String orderId, final ProgressResponseBody.ProgressListener progressListener, final ProgressRequestBody.ProgressRequestListener progressRequestListener) throws ApiException {
-        Object localVarPostBody = null;
+        Object localVarPostBody = new Object();
 
         // create path and map variables
         String localVarPath = "/store/order/{order_id}"
@@ -181,7 +181,7 @@ public void onRequestProgress(long bytesWritten, long contentLength, boolean don
      * @throws ApiException If fail to serialize the request body object
      */
     public com.squareup.okhttp.Call getInventoryCall(final ProgressResponseBody.ProgressListener progressListener, final ProgressRequestBody.ProgressRequestListener progressRequestListener) throws ApiException {
-        Object localVarPostBody = null;
+        Object localVarPostBody = new Object();
 
         // create path and map variables
         String localVarPath = "/store/inventory";
@@ -295,7 +295,7 @@ public void onRequestProgress(long bytesWritten, long contentLength, boolean don
      * @throws ApiException If fail to serialize the request body object
      */
     public com.squareup.okhttp.Call getOrderByIdCall(Long orderId, final ProgressResponseBody.ProgressListener progressListener, final ProgressRequestBody.ProgressRequestListener progressRequestListener) throws ApiException {
-        Object localVarPostBody = null;
+        Object localVarPostBody = new Object();
 
         // create path and map variables
         String localVarPath = "/store/order/{order_id}"
diff --git a/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/api/UserApi.java b/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/api/UserApi.java
index 518d851e31a..99532edeec8 100644
--- a/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/api/UserApi.java
+++ b/samples/client/petstore/java/okhttp-gson/src/main/java/io/swagger/client/api/UserApi.java
@@ -417,7 +417,7 @@ public void onRequestProgress(long bytesWritten, long contentLength, boolean don
      * @throws ApiException If fail to serialize the request body object
      */
     public com.squareup.okhttp.Call deleteUserCall(String username, final ProgressResponseBody.ProgressListener progressListener, final ProgressRequestBody.ProgressRequestListener progressRequestListener) throws ApiException {
-        Object localVarPostBody = null;
+        Object localVarPostBody = new Object();
 
         // create path and map variables
         String localVarPath = "/user/{username}"
@@ -536,7 +536,7 @@ public void onRequestProgress(long bytesWritten, long contentLength, boolean don
      * @throws ApiException If fail to serialize the request body object
      */
     public com.squareup.okhttp.Call getUserByNameCall(String username, final ProgressResponseBody.ProgressListener progressListener, final ProgressRequestBody.ProgressRequestListener progressRequestListener) throws ApiException {
-        Object localVarPostBody = null;
+        Object localVarPostBody = new Object();
 
         // create path and map variables
         String localVarPath = "/user/{username}"
@@ -660,7 +660,7 @@ public void onRequestProgress(long bytesWritten, long contentLength, boolean don
      * @throws ApiException If fail to serialize the request body object
      */
     public com.squareup.okhttp.Call loginUserCall(String username, String password, final ProgressResponseBody.ProgressListener progressListener, final ProgressRequestBody.ProgressRequestListener progressRequestListener) throws ApiException {
-        Object localVarPostBody = null;
+        Object localVarPostBody = new Object();
 
         // create path and map variables
         String localVarPath = "/user/login";
@@ -793,7 +793,7 @@ public void onRequestProgress(long bytesWritten, long contentLength, boolean don
      * @throws ApiException If fail to serialize the request body object
      */
     public com.squareup.okhttp.Call logoutUserCall(final ProgressResponseBody.ProgressListener progressListener, final ProgressRequestBody.ProgressRequestListener progressRequestListener) throws ApiException {
-        Object localVarPostBody = null;
+        Object localVarPostBody = new Object();
 
         // create path and map variables
         String localVarPath = "/user/logout";