ResponseClass is not translated to a response when converting 1.1 spec to 2.0 or 3.0

Description

When trying to convert a swagger 1.1 spec to 2.0 or 3.0 all the responses are missing response bodies. (A GET end-point that should return something only lists the error responses)

For example:

This part of the 1.1 spec has a responseClass field of type Channel

"path": "/channels/{channelId}",
            "description": "Active channel",
            "operations": [
                {
                    "httpMethod": "GET",
                    "summary": "Channel details.",
                    "nickname": "get",
                    "responseClass": "Channel",
                    "parameters": [
                        {
                            "name": "channelId",
                            "description": "Channel's id",
                            "paramType": "path",
                            "required": true,
                            "allowMultiple": false,
                            "dataType": "string"
                        }
                    ],
                    "errorResponses": [
                        {
                            "code": 404,
                            "reason": "Channel not found"
                        }
                    ]
                },

But the generated 2.0 spec has no response with a body

"/channels/{channelId}" : {
      "get" : {
        "tags" : [ "api-docschannels.{format}" ],
        "summary" : "Channel details.",
        "operationId" : "get",
        "parameters" : [ {
          "name" : "channelId",
          "in" : "path",
          "description" : "Channel's id",
          "required" : true,
          "type" : "string"
        } ],
        "responses" : {
          "404" : {
            "description" : "Channel not found"
          }
        }
      },

I would expect something like this to be present in the 2.0 variant

      "responses": {
          "200": {
            "description": "Some description",
            "schema": {
              "$ref": "#/definitions/Channel"
            }            
          },

How can I fix this problem, or is there another way to upgrade my 1.1 spec to a higher version so that the newer codegenerators will work with it?

Swagger-codegen version

I've tried 2.4.0, 2.3.1 and 3.0.0

Swagger declaration file content or url

See above

Command line used for generation

java -jar .\swagger-codegen-cli.jar generate -i ./resources.json -l swagger -o ./swagger

Where resources.json has the BasePath "." and lists all the apis that are in json files in the same directory.

Steps to reproduce

1. Input a 1.1 swagger spec file with at least one path that contains a responseClass
2. Generate the 2.0 or 3.0 swagger spec
3. The output swagger file has no response body

Run the listed Java swagger-codegen command with a Swagger 1.1 input containing responseClass. Trace the 1.1-to-2.0/3.0 conversion handling for responseClass, then verify that the generated document includes a success response whose schema references #/definitions/Channel alongside the existing error response.