Fix multipart requests for container types

Author: sermler

modules/openapi-generator/src/main/resources/typescript-fetch/apis.mustache

@@ -268,7 +268,12 @@ export class {{classname}} extends runtime.BaseAPI {
             {{/isEnumRef}}
             {{^isEnumRef}}
             {{^withoutRuntimeChecks}}
+            {{^isContainer}}
             formParams.append('{{baseName}}', new Blob([JSON.stringify({{{dataType}}}ToJSON(requestParameters['{{paramName}}']))], { type: "application/json", }));
+            {{/isContainer}}
+            {{#isContainer}}
+            formParams.append('{{baseName}}', new Blob([JSON.stringify(requestParameters['{{paramName}}'])], { type: "application/json", }));
+            {{/isContainer}}
             {{/withoutRuntimeChecks}}{{#withoutRuntimeChecks}}
             formParams.append('{{baseName}}', new Blob([JSON.stringify(requestParameters['{{paramName}}'])], { type: "application/json", }));
             {{/withoutRuntimeChecks}}