AttributeError: 'NoneType' when trying to access the admin panel view list about django-rules HOT 1 OPEN

class ObjectPermissionsMixin:
    def get_queryset(self, request):
        queryset = super().get_queryset(request)
        if request.user.is_superuser:
            return queryset
        return queryset.filter(pk__in=[item.pk for item in queryset if self.has_view_permission(request, item)])

    def has_permission(self, request, obj, perm_type):
        if not obj:
            return True
        codename = get_permission_codename(perm_type, self.opts)
        permission = f"{self.opts.app_label}.{codename}"
        return request.user.has_perm(permission, obj)

    def has_view_permission(self, request, obj=None):
        return self.has_permission(request, obj, 'view') or self.has_change_permission(request, obj)

    def has_change_permission(self, request, obj=None):
        return self.has_permission(request, obj, 'change')

    def has_delete_permission(self, request, obj=None):
        return self.has_permission(request, obj, 'delete')

@admin.register(Provider)
class ProviderAdmin(ObjectPermissionsMixin, ModelAdmin):