code: protected void send(JSONObject json, ResponseListener listener) {
          String contentType = headers.get(CONTENT_TYPE);
  
          if (contentType == null) {
              contentType = JSON_CONTENT_TYPE;
          }
  
          RequestBody body = RequestBody.create(MediaType.parse(contentType), json.toString());
  
          sendRequest(null, listener, body);
      }
docs: Send this resource request asynchronously, with the given JSON object as the request body.
  If the Content-Type header was not previously set, this method will set it to "application/json".
  
  @param json      The JSON object to put in the request body
  @param listener  The listener whose onSuccess or onFailure methods will be called when this request finishes