'The `UniqueTogetherValidator` always forces an implied \'required\'
state on the fields it applies to.'

def enforce_required_fields(self, attrs):

    if (self.instance is not None):
        return
    missing_items = {field_name: self.missing_message for field_name in self.fields if (field_name not in attrs)}
    if missing_items:
        raise ValidationError(missing_items, code=u'required')
