[vala] glib-2.0: Mark OptionEntry.arg_description as nullable

[Luca Bruno <lucabru src gnome org>]

commit 87483c1d3b22013206c316bee217422058f38bb1
Author: Alexander Kurtz <kurtz alex googlemail com>
Date:   Thu Feb 2 13:47:26 2012 +0100

    glib-2.0: Mark OptionEntry.arg_description as nullable
    
    Fixes bug 669241.

 vapi/glib-2.0.vapi |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/vapi/glib-2.0.vapi b/vapi/glib-2.0.vapi
index 9cd49a0..45f5640 100644
--- a/vapi/glib-2.0.vapi
+++ b/vapi/glib-2.0.vapi
@@ -3335,7 +3335,7 @@ namespace GLib {
 		public void* arg_data;
 
 		public unowned string description;
-		public unowned string arg_description;
+		public unowned string? arg_description;
 	}
 
 	[Compact]