def add_to_moderators(self, user, light_user=None):
        """Adds user to moderators and returns 'normal' or 'light'
        if it really added him.
        In case if user already was a moderator, returns None."""

        if not self.is_moderator(user, light_user):
            if user.is_authenticated():
                Moderator.objects.create(changelog=self, user=user)
                return 'normal'
            else:
                if light_user is not None:
                    self.light_moderators.create(light_user=light_user)
                    return 'light'