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

[Bilal Elmoussaoui <bilelmoussaoui src gnome org>]

commit 77f7caf18d877b0f997081dff8005127c7deb49e
Author: Bilal Elmoussaoui <bil elmoussaoui gmail com>
Date:   Sat Jan 1 18:26:40 2022 +0100

    gtk: mark gtk_glarea_get_context as nullable

 gtk/gtkglarea.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/gtk/gtkglarea.c b/gtk/gtkglarea.c
index 655c102cd7..de7cc7fa0f 100644
--- a/gtk/gtkglarea.c
+++ b/gtk/gtkglarea.c
@@ -1317,7 +1317,7 @@ gtk_gl_area_set_auto_render (GtkGLArea *area,
  *
  * Retrieves the `GdkGLContext` used by @area.
  *
- * Returns: (transfer none): the `GdkGLContext`
+ * Returns: (transfer none) (nullable): the `GdkGLContext`
  */
 GdkGLContext *
 gtk_gl_area_get_context (GtkGLArea *area)