title: POST @RequestParam Map<String, String> in Spring MVC returns empty map
body: <p>I have the following method:</p>
  
  <pre><code>@Controller
  public class InterfaceController extends MasterController
  {
      @PostMapping(value = "/interface") 
      @ResponseBody
      public String incomingPost(@RequestParam Map&lt;String, String&gt; queryMap)
      {
          System.out.println("Map: " + new Gson().toJson(queryMap));
          return "Raw string to return.";
      }
  }
  </code></pre>
  
  <p>When I make a POST request to <code>/interface</code>, I get a successful 200 response with the dummy string I want to return with but the Map is not populated with my parameters:</p>
  
  <pre><code>Map: {}
  </code></pre>
  
  <p>Why?</p>