#vulnerable code 
                              @Override
  public void onClose(Status status, Metadata trailers) {
    if (status.getCode() == Status.Code.CANCELLED
        && status.getDescription().contains(TIMEOUT_CANCEL_MSG)) {
      // If this was canceled because of handleTimeout(). The cancel is immediately retried or
      // completed in another fashion.
      return;
    }
    super.onClose(status, trailers);
  } 
                            #location 4 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                              @Override
  public void onClose(Status status, Metadata trailers) {
    if (status.getCode() == Status.Code.CANCELLED
        && status.getDescription() != null
        && status.getDescription().contains(TIMEOUT_CANCEL_MSG)) {
      // If this was canceled because of handleTimeout(). The cancel is immediately retried or
      // completed in another fashion.
      return;
    }
    super.onClose(status, trailers);
  }