title: Message "can't parse JSON. Raw result:" added to response body
body: <p>I'm trying to define a file download endpoint using the OpenAPI spec (v3).  I am facing two problems.
  1) the file is not being downloaded
  2) within swagger-ui, the response body shows a message that isn't produced by the server (i.e. can't parse JSON. Raw result:"</p>
  
  <p>Anyone have a clue as to what I am doing wrong?</p>
  
  <p>YAML code snapshot:
  <a href="https://i.stack.imgur.com/RjFaI.png" rel="noreferrer"><img src="https://i.stack.imgur.com/RjFaI.png" alt="enter image description here"></a></p>
  
  <p>Output result from swagger-ui running on an AWS server.
  <a href="https://i.stack.imgur.com/5LEXb.png" rel="noreferrer"><img src="https://i.stack.imgur.com/5LEXb.png" alt="enter image description here"></a></p>