def get_serializer(self, *args, **kwargs):
        serializer = super(FileViewSet, self).get_serializer(*args, **kwargs)
        if not isinstance(serializer, ListSerializer):
            try:
                organization = OrganizationMembership.objects.get_primary(self.request.user).organization
                serializer.fields['sub_matter'].queryset = SubMatter.objects.filter(collaborations__organization=organization)
            except OrganizationMembership.DoesNotExist:
                serializer.fields['sub_matter'].queryset = SubMatter.objects.none()
        return serializer