Sets this message flag as completed
        :param completition_date: the datetime this followUp was completed

def set_completed(self, *, completition_date=None):
        """ Sets this message flag as completed
        :param completition_date: the datetime this followUp was completed
        """
        self.__status = Flag.Complete
        completition_date = completition_date or dt.datetime.now()
        if completition_date.tzinfo is None:
            completition_date = self.protocol.timezone.localize(completition_date)
        self.__completed = completition_date
        self._track_changes()