[gtk+/gtk-3-18] Correct annotations for gtk_cell_layout_get_area

[Matthias Clasen <matthiasc src gnome org>]

commit a311eb6468e9639244cd5cd2a5e55abe5e609189
Author: Erika <rrika9 yahoo com>
Date:   Sun Dec 6 14:31:00 2015 +0000

    Correct annotations for gtk_cell_layout_get_area
    
    The function can return NULL.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=759081

 gtk/gtkcelllayout.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/gtk/gtkcelllayout.c b/gtk/gtkcelllayout.c
index 1f5253f..241f467 100644
--- a/gtk/gtkcelllayout.c
+++ b/gtk/gtkcelllayout.c
@@ -600,7 +600,8 @@ gtk_cell_layout_get_cells (GtkCellLayout *cell_layout)
  * if called on a #GtkCellArea or might be %NULL if no #GtkCellArea
  * is used by @cell_layout.
  *
- * Returns: (transfer none): the cell area used by @cell_layout.
+ * Returns: (transfer none) (nullable): the cell area used by @cell_layout,
+ * or %NULL in case no cell area is used.
  *
  * Since: 3.0
  */