gtk: mark buildable_get_id as nullable

the vfunc can return a nullable

diff --git a/gtk/gtkbuildable.c b/gtk/gtkbuildable.c
index 1eb45c03081392eba418e2a9cc3ba0140264cc83..bcd88171ad6351840cc0d85cceb1f22284eaae36 100644 (file)
--- 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)