diff --git a/pkg/schema/type_check.go b/pkg/schema/type_check.go
index e6590bcea..9b6e18e15 100644
--- a/pkg/schema/type_check.go
+++ b/pkg/schema/type_check.go
@@ -33,6 +33,9 @@ func (ts *TypeSystem) GetFullRecursiveSubjectTypesForRelation(ctx context.Contex
 	if err != nil {
 		return nil, err
 	}
+	if set == nil {
+		return nil, nil
+	}
 	set.Merge(nonTerminals)
 	return set.AsSlice(), nil
 }