@Override
 public void onResponse(Object response) {
   executionCallback.onResponse(toObject(response));
 }
 @Override
 public void onFailure(Throwable t) {
   executionCallback.onFailure(t);
 }
 private void notifyCallback(boolean result) {
   if (callback != null) {
     callback.onResponse(result);
   }
 }