[gtk+/gtk-3-22] Button: Annotate set_image() argument as nullable

[Daniel Boles <dboles src gnome org>]

commit 701f82d1c3192fde4a18ee7cd686837ddd798c7b
Author: Daniel Boles <dboles src gnome org>
Date:   Sun Sep 24 22:20:34 2017 +0100

    Button: Annotate set_image() argument as nullable
    
    Passing NULL is valid and results in the image child being unset/removed

 gtk/gtkbutton.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/gtk/gtkbutton.c b/gtk/gtkbutton.c
index b39d55b..90e1a5d 100644
--- a/gtk/gtkbutton.c
+++ b/gtk/gtkbutton.c
@@ -2543,7 +2543,7 @@ gtk_button_grab_notify (GtkWidget *widget,
 /**
  * gtk_button_set_image:
  * @button: a #GtkButton
- * @image: a widget to set as the image for the button
+ * @image: (nullable): a widget to set as the image for the button, or %NULL to unset
  *
  * Set the image of @button to the given widget. The image will be
  * displayed if the label text is %NULL or if