def _flush_data(self):
        """
        If this relation's local unit data has been modified, publish it on the
        relation. This should be automatically called.
        """
        if self._data and self._data.modified:
            hookenv.relation_set(self.relation_id, dict(self.to_publish.data))
If this relation's local unit data has been modified, publish it on the
        relation. This should be automatically called.