chore: handle nil options for transaction runner

retry.go

@@ -32,14 +32,12 @@ import (
 // gorm database, and retries the transaction if it is aborted by Spanner.
 func RunTransaction(ctx context.Context, db *gorm.DB, fc func(tx *gorm.DB) error, opts ...*sql.TxOptions) error {
 	// Disable internal (checksum-based) retries on the Spanner database/SQL connection.
-	var opt *sql.TxOptions
 	// Note: gorm also only uses the first option, so it is safe to pick just the first element in the slice.
-	if len(opts) > 0 {
-		opt = opts[0]
+	if len(opts) > 0 && opts[0] != nil {
+		opts[0].Isolation = spannerdriver.WithDisableRetryAborts(opts[0].Isolation)
 	}
-	opt.Isolation = spannerdriver.WithDisableRetryAborts(opt.Isolation)
 	for {
-		err := db.Transaction(fc, opt)
+		err := db.Transaction(fc, opts...)
 		if err == nil {
 			return nil
 		}

spanner_test.go

@@ -245,7 +245,7 @@ func TestRunTransaction(t *testing.T) {
 			return err
 		}
 		return nil
-	}, &sql.TxOptions{}); err != nil {
+	}); err != nil {
 		t.Fatal(err)
 	}
 	// Verify that the insert was only executed once.
@@ -282,6 +282,20 @@ func TestRunTransaction(t *testing.T) {
 	}
 }
 
+func TestRunTransactionWithNilAsOptions(t *testing.T) {
+	t.Parallel()
+
+	ctx := context.Background()
+	db, _, teardown := setupTestGormConnection(t)
+	defer teardown()
+
+	if err := RunTransaction(ctx, db, func(tx *gorm.DB) error {
+		return nil
+	}, nil); err != nil {
+		t.Fatal(err)
+	}
+}
+
 func filter(requests []interface{}, sql string) (ret []*spannerpb.ExecuteSqlRequest) {
 	for _, i := range requests {
 		if req, ok := i.(*spannerpb.ExecuteSqlRequest); ok {