code: protected void onSuccess(AsyncRequest<D, RQ> asyncRequest, ResponseStatus status) {
      final WriteResponse response = WriteResponse.EMPTY;
      for (final AsyncRequest.Thunk thunk: asyncRequest.getThunks()) {
        WriteCallback callback = (WriteCallback) thunk.callback;
        callback.onSuccess(new WriteResponse() {
          @Override
          public Object getRawResponse() {
            return response.getRawResponse();
          }
  
          @Override
          public String getStringResponse() {
            return response.getStringResponse();
          }
  
          @Override
          public long bytesWritten() {
            return thunk.sizeInBytes;
          }
        });
      }
    }
docs: Callback on sending the asyncRequest successfully