[gitg] Make the view's stack_panel property nullable

[Ignacio Casal Quinteiro <icq src gnome org>]

commit 671d2f7a2bb9cf4e23baefb9a1a2693e1323e9ca
Author: Techlive Zheng <techlivezheng gmail com>
Date:   Fri May 31 01:18:53 2013 +0800

    Make the view's stack_panel property nullable

 libgitg-ext/gitg-ext-view.vala    |    4 ++--
 plugins/history/gitg-history.vala |    2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)
---
diff --git a/libgitg-ext/gitg-ext-view.vala b/libgitg-ext/gitg-ext-view.vala
index 6c742c4..0264add 100644
--- a/libgitg-ext/gitg-ext-view.vala
+++ b/libgitg-ext/gitg-ext-view.vala
@@ -92,10 +92,10 @@ public interface View : Object, UIElement
         * A Gtk Builder element that the panel plugins will be
         * populated into.
         *
-        * @return Gtk.Stack
+        * @return Gtk.Stack?
         *
         */
-       public abstract Gtk.Stack stack_panel { get; }
+       public abstract Gtk.Stack? stack_panel { get; }
 }
 
 }
diff --git a/plugins/history/gitg-history.vala b/plugins/history/gitg-history.vala
index 8b3d905..b4db53b 100644
--- a/plugins/history/gitg-history.vala
+++ b/plugins/history/gitg-history.vala
@@ -45,7 +45,7 @@ namespace GitgHistory
                        owned get { return "/org/gnome/gitg/Views/History"; }
                }
 
-               public Gtk.Stack stack_panel
+               public Gtk.Stack? stack_panel
                {
                        get { return d_stack_panel; }
                }