code: async def _handle_watermark_notification(self, watermark_notification):
          
          conv_id = watermark_notification.conversation_id.id
          res = parsers.parse_watermark_notification(watermark_notification)
          await self.on_watermark_notification.fire(res)
          try:
              conv = await self._get_or_fetch_conversation(conv_id)
          except exceptions.NetworkError:
              logger.warning(
                  'Failed to fetch conversation for watermark notification: %s',
                  conv_id
              )
          else:
              await conv.on_watermark_notification.fire(res)
docs: Receive WatermarkNotification and update the conversation.
  
          Args:
              watermark_notification: hangouts_pb2.WatermarkNotification instance