[gtk/bilelmoussaoui/g-i] gtk: mark gtk_mount_operation_get_parent as nullable

[Bilal Elmoussaoui <bilelmoussaoui src gnome org>]

commit d029b62d233730f092d1ebaae3f8ea11052629ed
Author: Bilal Elmoussaoui <bil elmoussaoui gmail com>
Date:   Sat Jan 1 19:05:33 2022 +0100

    gtk: mark gtk_mount_operation_get_parent as nullable

 gtk/gtkmountoperation.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/gtk/gtkmountoperation.c b/gtk/gtkmountoperation.c
index baa4f785e5..43760283b4 100644
--- a/gtk/gtkmountoperation.c
+++ b/gtk/gtkmountoperation.c
@@ -1873,7 +1873,7 @@ gtk_mount_operation_set_parent (GtkMountOperation *op,
  *
  * Gets the transient parent used by the `GtkMountOperation`.
  *
- * Returns: (transfer none): the transient parent for windows shown by @op
+ * Returns: (transfer none) (nullable): the transient parent for windows shown by @op
  */
 GtkWindow *
 gtk_mount_operation_get_parent (GtkMountOperation *op)