[gtk/headless-seatless: 16/21] docs: Clarify gdk_display_get_default_seat() docs

[Matthias Clasen <matthiasc src gnome org>]

commit a5def45ea45dc4ba5181e5944e7c877d8045bf63
Author: Matthias Clasen <mclasen redhat com>
Date:   Thu May 14 23:14:04 2020 -0400

    docs: Clarify gdk_display_get_default_seat() docs
    
    This function can return %NULL if the display
    does not have a seat. Document that.

 gdk/gdkdisplay.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)
---
diff --git a/gdk/gdkdisplay.c b/gdk/gdkdisplay.c
index 9274ca1318..f99128459e 100644
--- a/gdk/gdkdisplay.c
+++ b/gdk/gdkdisplay.c
@@ -1497,7 +1497,10 @@ gdk_display_remove_seat (GdkDisplay *display,
  *
  * Returns the default #GdkSeat for this display.
  *
- * Returns: (transfer none): the default seat.
+ * Note that a display may not have a seat. In this case,
+ * this function will return %NULL.
+ *
+ * Returns: (transfer none) (nullable): the default seat.
  **/
 GdkSeat *
 gdk_display_get_default_seat (GdkDisplay *display)