use model class for request body with additionalProperties (#16613)

* try out simple fix

* add test case

* generate samples

samples/client/petstore/javascript-promise-es6/docs/FakeApi.md

@@ -19,6 +19,7 @@ Method | HTTP request | Description
 [**testEnumParameters**](FakeApi.md#testEnumParameters) | **GET** /fake | To test enum parameters
 [**testGroupParameters**](FakeApi.md#testGroupParameters) | **DELETE** /fake | Fake endpoint to test group parameters (optional)
 [**testInlineAdditionalProperties**](FakeApi.md#testInlineAdditionalProperties) | **POST** /fake/inline-additionalProperties | test inline additionalProperties
+[**testInlineFreeformAdditionalProperties**](FakeApi.md#testInlineFreeformAdditionalProperties) | **POST** /fake/inline-freeform-additionalProperties | test inline free-form additionalProperties
 [**testJsonFormData**](FakeApi.md#testJsonFormData) | **GET** /fake/jsonFormData | test json serialization of form data
 [**testQueryParameterCollectionFormat**](FakeApi.md#testQueryParameterCollectionFormat) | **PUT** /fake/test-query-parameters | 
 
@@ -758,6 +759,50 @@ No authorization required
 - **Accept**: Not defined
 
 
+## testInlineFreeformAdditionalProperties
+
+> testInlineFreeformAdditionalProperties(testInlineFreeformAdditionalPropertiesRequest)
+
+test inline free-form additionalProperties
+
+
+
+### Example
+
+```javascript
+import OpenApiPetstore from 'open_api_petstore';
+
+let apiInstance = new OpenApiPetstore.FakeApi();
+let testInlineFreeformAdditionalPropertiesRequest = new OpenApiPetstore.TestInlineFreeformAdditionalPropertiesRequest(); // TestInlineFreeformAdditionalPropertiesRequest | request body
+apiInstance.testInlineFreeformAdditionalProperties(testInlineFreeformAdditionalPropertiesRequest).then(() => {
+  console.log('API called successfully.');
+}, (error) => {
+  console.error(error);
+});
+
+```
+
+### Parameters
+
+
+Name | Type | Description  | Notes
+------------- | ------------- | ------------- | -------------
+ **testInlineFreeformAdditionalPropertiesRequest** | [**TestInlineFreeformAdditionalPropertiesRequest**](TestInlineFreeformAdditionalPropertiesRequest.md)| request body | 
+
+### Return type
+
+null (empty response body)
+
+### Authorization
+
+No authorization required
+
+### HTTP request headers
+
+- **Content-Type**: application/json
+- **Accept**: Not defined
+
+
 ## testJsonFormData
 
 > testJsonFormData(param, param2)

samples/client/petstore/javascript-promise-es6/docs/TestInlineFreeformAdditionalPropertiesRequest.md

@@ -0,0 +1,9 @@
+# OpenApiPetstore.TestInlineFreeformAdditionalPropertiesRequest
+
+## Properties
+
+Name | Type | Description | Notes
+------------ | ------------- | ------------- | -------------
+**someProperty** | **String** |  | [optional] 
+
+