code: def clean(self):
          
          cleaned_data = super(MastodonForm, self).clean()
          tag = cleaned_data.get("tag")
          screen = cleaned_data.get("tooter")
          # check if one of the field is filled when a field is empty the clean() function set it as None
          if tag is None and screen is None:
              raise ValidationError(_("You have to fill ONE of the fields (or tag + tooter or tooter + fav)"))
docs: validate if tag or screen is filled
          :return: