docs: def check_stops(pfeed, *, as_df=False, include_warnings=False):
      """
      Analog of :func:`check_frequencies` for ``pfeed.stops``
      """
      # Use gtfstk's stop validator
      if pfeed.stops is not None:
          stop_times = pd.DataFrame(columns=['stop_id'])
          feed = gt.Feed(stops=pfeed.stops, stop_times=stop_times,
            dist_units='km')
          return gt.check_stops(feed, as_df=as_df, include_warnings=False)