code: def _force_close(self, file_length=None):
      
      if file_length is None:
        file_length = self._get_offset_from_gcs() + 1
      self._send_data('', 0, file_length)
docs: Close this buffer on file_length.
  
      Finalize this upload immediately on file_length.
      Contents that are still in memory will not be uploaded.
  
      This is a utility method that does not modify self.
  
      Args:
        file_length: file length. Must match what has been uploaded. If None,
          it will be queried from GCS.