code: def _SetExtractionPreferredTimeZone(self, knowledge_base):
      
      # Note session.preferred_time_zone will default to UTC but
      # self._preferred_time_zone is None when not set.
      if self._preferred_time_zone:
        try:
          knowledge_base.SetTimeZone(self._preferred_time_zone)
        except ValueError:
          # pylint: disable=protected-access
          logger.warning(
              'Unsupported time zone: {0:s}, defaulting to {1:s}'.format(
                  self._preferred_time_zone, knowledge_base._time_zone.zone))
docs: Sets the preferred time zone before extraction.
  
      Args:
        knowledge_base (KnowledgeBase): contains information from the source
            data needed for parsing.