use map/array model class only if it is generated (#17612)

* fix

* tests

* generate samples

* refactor

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

@@ -23,6 +23,7 @@ Method | HTTP request | Description
 [**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 | 
+[**testStringMapReference**](FakeApi.md#testStringMapReference) | **POST** /fake/stringMap-reference | test referenced string map
 
 
 
@@ -970,3 +971,48 @@ No authorization required
 - **Content-Type**: Not defined
 - **Accept**: Not defined
 
+
+## testStringMapReference
+
+> testStringMapReference(requestBody)
+
+test referenced string map
+
+
+
+### Example
+
+```javascript
+import OpenApiPetstore from 'open_api_petstore';
+
+let apiInstance = new OpenApiPetstore.FakeApi();
+let requestBody = {key: "null"}; // {String: String} | request body
+apiInstance.testStringMapReference(requestBody, (error, data, response) => {
+  if (error) {
+    console.error(error);
+  } else {
+    console.log('API called successfully.');
+  }
+});
+```
+
+### Parameters
+
+
+Name | Type | Description  | Notes
+------------- | ------------- | ------------- | -------------
+ **requestBody** | [**{String: String}**](String.md)| request body | 
+
+### Return type
+
+null (empty response body)
+
+### Authorization
+
+No authorization required
+
+### HTTP request headers
+
+- **Content-Type**: application/json
+- **Accept**: Not defined
+