title: Swagger/Swashbuckle showing "Unknown response type"
body: <p>I am creating an C# ASP.NET Core 2.0 REST API, all going well for the most part.  It is using MVC routing to gen the REST API.  The controllers are pretty simple.  </p>
  
  <pre><code>    // POST: api/Volume/{zoneID}/Set/{volume}
      [HttpPost("{zoneId:int}/[action]/{volume:int}", Name = "Set")]
      public IActionResult Set(int zoneId, int volume)
      {
          return CreateAndSend(strZonesLevel, zoneId, $"{volume:X2}");
  
      }
  </code></pre>
  
  <p>Using the latest of everything, installed Swagger/Swashbuckle for AspNetCore 2.3.0 and the UI comes up with the APIs and all.  The SwashBuckle UI works well, I can test the API etc.</p>
  
  <p>The one exception is that on the UI, the Response type ALWAYS comes back as "Unknown Response Type."</p>
  
  <p><a href="https://i.stack.imgur.com/6qqBh.jpg" rel="nofollow noreferrer">https://i.stack.imgur.com/6qqBh.jpg</a></p>
  
  <p>I have the following attributes in front of my class (all methods return the same type)</p>
  
  <pre><code>[Produces("application/json")]
  [Route("api/Volume")]
  [ProducesResponseType(typeof(ControllerResponseModel), 200)]
  [ProducesResponseType(typeof(ControllerResponseModel), 400)]
  [ProducesResponseType(typeof(ControllerResponseModel), 500)] 
  </code></pre>
  
  <p>The generated JSON seems allright, the ControllerResponseModel is in the definition, and referenced in all the right places by the Volume API.  Here is a subset.</p>
  
  <pre><code>{
    "swagger": "2.0",
    "info": {
      "version": "v1",
      "title": "AVController API"
    },
    "paths": {
      "/api/Volume/{zoneId}/Set/{volume}": {
        "post": {
          "tags": ["Volume"],
          "operationId": "ApiVolumeByZoneIdSetByVolumePost",
          "consumes": [],
          "produces": ["application/json"],
          "parameters": [
            {
              "name": "zoneId",
              "in": "path",
              "required": true,
              "type": "integer",
              "format": "int32"
            },
            {
              "name": "volume",
              "in": "path",
              "required": true,
              "type": "integer",
              "format": "int32"
            }
          ],
          "responses": {
            "200": {
              "description": "Success",
              "schema": {
                "type": "array",
                "items": { "$ref": "#/definitions/ControllerResponseModel" }
              }
            },
            "400": {
              "description": "Bad Request",
              "schema": {
                "type": "array",
                "items": { "$ref": "#/definitions/ControllerResponseModel" }
              }
            },
            "500": {
              "description": "Server Error",
              "schema": {
                "type": "array",
                "items": { "$ref": "#/definitions/ControllerResponseModel" }
              }
            }
          }
        }
      }
    },
    "definitions": {
      "ControllerResponseModel": {
        "type": "object",
        "properties": {
          "command": { "type": "string" },
          "message": { "type": "string" },
          "url": { "type": "string" }
        }
      }
    }
  }
  </code></pre>
  
  <p>Any ideas why the UI would not be showing the return type and value?  I have tried numerous things, like using gets instead of posts as well as using the [SwaggerResponse] attributes, but the results are the same.</p>