docs: def _ensure_slack(self, connector: Any, retries: int,
                        backoff: Callable[[int], float]) -> None:
          """ Ensure we have a SlackClient. """
          connector = self._env_var if connector is None else connector
          slack: SlackClient = _create_slack(connector)
          self._slack = _SlackClientWrapper(
              slack=slack,
              retries=retries,
              backoff=backoff
          )