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

[Bilal Elmoussaoui <bilelmoussaoui src gnome org>]

commit 30d8c8e17c58e96c788e03930f9fce83e7f4c9a4
Author: Bilal Elmoussaoui <bil elmoussaoui gmail com>
Date:   Sat Jan 1 18:12:05 2022 +0100

    gtk: mark buildable_get_id as nullable
    
    the vfunc can return a nullable

 gtk/gtkbuildable.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/gtk/gtkbuildable.c b/gtk/gtkbuildable.c
index 1eb45c0308..bcd88171ad 100644
--- a/gtk/gtkbuildable.c
+++ b/gtk/gtkbuildable.c
@@ -83,7 +83,7 @@ gtk_buildable_set_buildable_id (GtkBuildable *buildable,
  * `GtkBuilder` sets the name based on the ID attribute
  * of the <object> tag used to construct the @buildable.
  *
- * Returns: the ID of the buildable object
+ * Returns: (nullable): the ID of the buildable object
  **/
 const char *
 gtk_buildable_get_buildable_id (GtkBuildable *buildable)