[JavaScript] returnType = null when used with "allOf"

Hi,

Description

Using JavaScript codegen I got null data when endpoint response definition has allOf.

Swagger-codegen version

2.3.1

Swagger declaration file content or url

"/item-categories": {
      "get": {
        "operationId": "findItemCategories",
        "responses": {
          "200": {
            "description": "",
            "schema": {
              "allOf": [
                {
                  "type": "object",
                  "properties": {
                    "results": {
                      "type": "array",
                      "items": {
                        "$ref": "#/definitions/item-category-output"
                      }
                    }
                  },
                  "required": [
                    "results"
                  ]
                },
                {
                  "$ref": "./common.oas2.yml#/definitions/standard-list-result"
                }
              ]
            }
          }
        }
      }

Suggest a fix/enhancement

I see that generated code has following part causing this for those endpoints:

var returnType = BackgroundOutputDetailed;

Thanks,

Start with the JavaScript code generated for the supplied /item-categories response and inspect how the allOf schema is converted into the returnType assignment. Reproduce the null return type with the shown Swagger declaration, then verify that a suitable non-null response type is generated for this endpoint.