title: Springfox / Swagger does not resolve polymorphic field
body: <p>I'm having a simple Spring Boot application with one REST endpoint to return a "Job" object, which contains a list of polymorphics, next to other stuff. 
  We go Code First approach and try to create the API models to fit our needs. But the generated Api Doc does not represent our model the in it's full complexity, as it does not resolve the list of polymorphics.</p>
  
  <p>The Job object looks like</p>
  
  <pre><code>@Data // Lombok Getters and Setters
  public final class Job {
      private String foo;
      private String bar;
      private List&lt;Condition&gt; conditionList;
  }
  </code></pre>
  
  <p>Condition is a parent object for a set of different conditions</p>
  
  <pre><code>public abstract class Condition {
  
  }
  </code></pre>
  
  <p>Two example implementations of a Condition would be</p>
  
  <pre><code>@Data
  public final class Internal extends Condition {
      private String nodeId;
  }
  </code></pre>
  
  <p>and</p>
  
  <pre><code>@Data
  public final class Timed extends Condition {
      private ZonedDateTime timestamp;
  }
  </code></pre>
  
  <p>The REST controller is stupidly simple:</p>
  
  <pre><code>@RestController
  @RequestMapping("/hello")
  public class MyController {
  
      @GetMapping
      public ResponseEntity&lt;Job&gt; getJob() {
          return new ResponseEntity&lt;&gt;(new Job(), HttpStatus.OK);
      }
  }
  </code></pre>
  
  <p>Now, when I open the Swagger UI and look at the generated definition, the element <code>conditionList</code> is an empty object <code>{}</code></p>
  
  <p>I tried to use the @JsonSubTypes and @ApiModel on the classed, but there was no difference in the output. I might not have used them correctly, or maybe Swagger is just not able to fulfill the job, or maybe I'm just blind or stupid.</p>
  
  <p>How can I get Swagger to include the Subtypes into the generated api doc?</p>