code: async def _on_event(self, event_):
          
          conv_id = event_.conversation_id.id
          try:
              conv = await self._get_or_fetch_conversation(conv_id)
          except exceptions.NetworkError:
              logger.warning(
                  'Failed to fetch conversation for event notification: %s',
                  conv_id
              )
          else:
              self._sync_timestamp = parsers.from_timestamp(event_.timestamp)
              conv_event = conv.add_event(event_)
              # conv_event may be None if the event was a duplicate.
              if conv_event is not None:
                  await self.on_event.fire(conv_event)
                  await conv.on_event.fire(conv_event)
docs: Receive a hangouts_pb2.Event and fan out to Conversations.
  
          Args:
              event_: hangouts_pb2.Event instance