code: @Override public final InputStream getErrorStream() {
      try {
        HttpEngine response = getResponse();
        if (HttpEngine.hasBody(response.getResponse())
            && response.getResponse().code() >= HTTP_BAD_REQUEST) {
          return response.getResponse().body().byteStream();
        }
        return null;
      } catch (IOException e) {
        return null;
      }
    }
docs: Returns an input stream from the server in the case of error such as the
  requested file (txt, htm, html) is not found on the remote server.