[gtk/bilelmoussaoui/g-i] g-i: mark GtkSnapshot to_(node|paintable) as nullable

[Bilal Elmoussaoui <bilelmoussaoui src gnome org>]

commit b362eeefdf1acb811789ce415aca99b48fca8287
Author: Bilal Elmoussaoui <bil elmoussaoui gmail com>
Date:   Sun Jan 23 22:11:07 2022 +0000

    g-i: mark GtkSnapshot to_(node|paintable) as nullable
    
    Fixes an upstream issue reported at https://github.com/gtk-rs/gtk4-rs/issues/845

 gtk/gtksnapshot.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)
---
diff --git a/gtk/gtksnapshot.c b/gtk/gtksnapshot.c
index 0c05ecad0e..cdf61845d5 100644
--- a/gtk/gtksnapshot.c
+++ b/gtk/gtksnapshot.c
@@ -302,7 +302,7 @@ gtk_snapshot_new (void)
  * Returns the node that was constructed by @snapshot
  * and frees @snapshot.
  *
- * Returns: (transfer full): a newly-created [class@Gsk.RenderNode]
+ * Returns: (transfer full) (nullable): a newly-created [class@Gsk.RenderNode]
  */
 GskRenderNode *
 gtk_snapshot_free_to_node (GtkSnapshot *snapshot)
@@ -324,7 +324,7 @@ gtk_snapshot_free_to_node (GtkSnapshot *snapshot)
  * Returns a paintable for the node that was
  * constructed by @snapshot and frees @snapshot.
  *
- * Returns: (transfer full): a newly-created [iface@Gdk.Paintable]
+ * Returns: (transfer full) (nullable): a newly-created [iface@Gdk.Paintable]
  */
 GdkPaintable *
 gtk_snapshot_free_to_paintable (GtkSnapshot           *snapshot,
@@ -1497,7 +1497,7 @@ gtk_snapshot_pop_collect (GtkSnapshot *snapshot)
  * add more nodes to @snapshot. The only function that should
  * be called after this is [method@GObject.Object.unref].
  *
- * Returns: (transfer full): the constructed `GskRenderNode`
+ * Returns: (transfer full) (nullable): the constructed `GskRenderNode`
  */
 GskRenderNode *
 gtk_snapshot_to_node (GtkSnapshot *snapshot)
@@ -1532,7 +1532,7 @@ gtk_snapshot_to_node (GtkSnapshot *snapshot)
  * add more nodes to @snapshot. The only function that should
  * be called after this is [method@GObject.Object.unref].
  *
- * Returns: (transfer full): a new `GdkPaintable`
+ * Returns: (transfer full) (nullable): a new `GdkPaintable`
  */
 GdkPaintable *
 gtk_snapshot_to_paintable (GtkSnapshot           *snapshot,