title: Swagger UI - " TypeError: Failed to fetch" on valid response
body: <p>I've just pulled down the latest Swagger from the Git repo (3.0.19) using: <a href="https://github.com/swagger-api/swagger-ui.git" rel="noreferrer">https://github.com/swagger-api/swagger-ui.git</a> and updated my API to use the new version.</p>
  
  <p>Ran <code>git describe --tags</code> to confirm and my version is currently: <code>v3.0.19-6-gaab1403</code></p>
  
  <p>The problem I'm having is one described <a href="https://github.com/swagger-api/swagger-ui/issues/2919" rel="noreferrer">here</a>, whereby my response is a 403 (I can see this in the inspector on the browser) and although I have a reponse for error 403, I still get the <code>TypeError: Failed to fetch</code> message.</p>
  
  <p><a href="https://i.stack.imgur.com/4AKLI.png" rel="noreferrer"><img src="https://i.stack.imgur.com/4AKLI.png" alt="enter image description here"></a></p>
  
  <p><a href="https://i.stack.imgur.com/FAUli.png" rel="noreferrer"><img src="https://i.stack.imgur.com/FAUli.png" alt="enter image description here"></a></p>
  
  <p>Here's a snippet from my definition regarding the 403 response:</p>
  
  <pre><code>                    "403": {
                      "description": "Forbidden",
                      "headers": {
                          "Access-Control-Allow-Origin": {
                              "type": "string"
                          }
                      }
                  },
  </code></pre>
  
  <p>I've also noticed it reported <a href="https://stackoverflow.com/questions/45150406/server-response-is-empty-on-swagger-ui">here</a> however, I know it's not a CORS issue as I have tested the endpoints and the OPTIONS are returning correct, as are the endpoints if called with valid information (I force this 403).</p>
  
  <p>Could anyone point me in the right direction please?</p>
  
  <p><strong>Update:</strong> I have since tested on a 401 response, with the same response. </p>
  
  <p><a href="https://i.stack.imgur.com/KkWXY.png" rel="noreferrer"><img src="https://i.stack.imgur.com/KkWXY.png" alt="enter image description here"></a></p>
  
  <p>And that a 400 is working as expected: </p>
  
  <p><a href="https://i.stack.imgur.com/VnT1g.png" rel="noreferrer"><img src="https://i.stack.imgur.com/VnT1g.png" alt="enter image description here"></a></p>