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

[Bilal Elmoussaoui <bilelmoussaoui src gnome org>]

commit a8a98523db79c38ef240da9c74f4fffa840f30fa
Author: Bilal Elmoussaoui <bil elmoussaoui gmail com>
Date:   Wed Feb 9 13:09:47 2022 +0000

    gdk: mark gdk_device_get_device_tool as nullable

 gdk/gdkdevice.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/gdk/gdkdevice.c b/gdk/gdkdevice.c
index 0c8973f460..541bdda939 100644
--- a/gdk/gdkdevice.c
+++ b/gdk/gdkdevice.c
@@ -1242,7 +1242,7 @@ gdk_device_get_num_touches (GdkDevice *device)
  *
  * Retrieves the current tool for @device.
  *
- * Returns: (transfer none): the `GdkDeviceTool`
+ * Returns: (transfer none) (nullable): the `GdkDeviceTool`
  */
 GdkDeviceTool *
 gdk_device_get_device_tool (GdkDevice *device)