Sometimes there's no `filterset_class` defined yet the client still
        requests a filter. Make sure they see an error too. This means
        we have to `get_filterset_kwargs()` even if there's no `filterset_class`.

def get_filterset(self, request, queryset, view):
        """
        Sometimes there's no `filterset_class` defined yet the client still
        requests a filter. Make sure they see an error too. This means
        we have to `get_filterset_kwargs()` even if there's no `filterset_class`.
        """
        # TODO: .base_filters vs. .filters attr (not always present)
        filterset_class = self.get_filterset_class(view, queryset)
        kwargs = self.get_filterset_kwargs(request, queryset, view)
        self._validate_filter(kwargs.pop('filter_keys'), filterset_class)
        if filterset_class is None:
            return None
        return filterset_class(**kwargs)