Check that all the filter[key] are valid.

        :param keys: list of FilterSet keys
        :param filterset_class: :py:class:`django_filters.rest_framework.FilterSet`
        :raises ValidationError: if key not in FilterSet keys or no FilterSet.

def _validate_filter(self, keys, filterset_class):
        """
        Check that all the filter[key] are valid.

        :param keys: list of FilterSet keys
        :param filterset_class: :py:class:`django_filters.rest_framework.FilterSet`
        :raises ValidationError: if key not in FilterSet keys or no FilterSet.
        """
        for k in keys:
            if ((not filterset_class) or (k not in filterset_class.base_filters)):
                raise ValidationError("invalid filter[{}]".format(k))