code: def _FormatMessage(self, event):
      
      message, _ = self._output_mediator.GetFormattedMessages(event)
      if message is None:
        data_type = getattr(event, 'data_type', 'UNKNOWN')
        raise errors.NoFormatterFound(
            'Unable to find event formatter for: {0:s}.'.format(data_type))
  
      return message
docs: Formats the message.
  
      Args:
        event (EventObject): event.
  
      Returns:
        str: message field.
  
      Raises:
        NoFormatterFound: if no event formatter can be found to match the data
            type in the event.