gtk: mark gtk_lock_button_get_permission as nullable

like the constructor/setter

diff --git a/gtk/gtklockbutton.c b/gtk/gtklockbutton.c
index 5862e866d8a99bba05019c6900499f9c78736be7..dda8cc91479f50a0850b432583d2c06aed150609 100644 (file)
--- a/gtk/gtklockbutton.c
+++ b/gtk/gtklockbutton.c
@@ -535,7 +535,7 @@ gtk_lock_button_new (GPermission *permission)
  *
  * Obtains the `GPermission` object that controls @button.
  *
- * Returns: (transfer none): the `GPermission` of @button
+ * Returns: (transfer none) (nullable): the `GPermission` of @button
  */
 GPermission *
 gtk_lock_button_get_permission (GtkLockButton *button)