Missing content type when serializing Responses that are references in v2 #1000

'/Tasks({Id})/Default.Upload':
    post:
      tags:
        - Tasks.Actions
      summary: Invoke action Upload
      operationId: Tasks.DocumentDto.Upload
+      produces:
+        - application/json
      parameters:
        - in: path
          name: Id
          description: 'key: Id of DocumentDto'
          required: true
          type: integer
          format: int32
          maximum: 2147483647
          minimum: -2147483648
          x-ms-docs-key-type: DocumentDto
      responses:
        '200':
          $ref: '#/responses/UploadResponse'
        default:
          $ref: '#/responses/error'
      x-ms-docs-operation-type: action
    x-description: Provides operations to call the Upload method.