code: def delete(self, reference, option=None):
          
          write_pb = _helpers.pb_for_delete(reference._document_path, option)
          self._add_write_pbs([write_pb])
docs: Add a "change" to delete a document.
  
          See
          :meth:`~.firestore_v1beta1.document.DocumentReference.delete` for
          more information on how ``option`` determines how the change is
          applied.
  
          Args:
              reference (~.firestore_v1beta1.document.DocumentReference): A
                 document reference that will be deleted in this batch.
              option (Optional[~.firestore_v1beta1.client.WriteOption]): A
                 write option to make assertions / preconditions on the server
                 state of the document before applying changes.