docs: def _cache_get_last_in_slice(url_dict, start_int, total_int, authn_subj_list):
      """Return None if cache entry does not exist."""
      key_str = _gen_cache_key_for_slice(url_dict, start_int, total_int, authn_subj_list)
      # TODO: Django docs state that cache.get() should return None on unknown key.
      try:
          last_ts_tup = django.core.cache.cache.get(key_str)
      except KeyError:
          last_ts_tup = None
      logging.debug('Cache get. key="{}" -> last_ts_tup={}'.format(key_str, last_ts_tup))
      return last_ts_tup