[gnome-mahjongg] Do not translate empty string

[Jiro Matsuzawa <jmatsuzawa src gnome org>]

commit fcea13b786d60eacdfa8318281aa33eebe54c622
Author: Jiro Matsuzawa <jmatsuzawa gnome org>
Date:   Tue Mar 19 15:26:02 2013 +0900

    Do not translate empty string
    
    Translating empty strings shows a po header entry. We must not gettext
    them.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=696043

 src/gnome-mahjongg.vala |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/src/gnome-mahjongg.vala b/src/gnome-mahjongg.vala
index e1bfb3e..7cec7a8 100644
--- a/src/gnome-mahjongg.vala
+++ b/src/gnome-mahjongg.vala
@@ -732,7 +732,7 @@ public class Mahjongg : Gtk.Application
 
         Gtk.init (ref args);
 
-        var context = new OptionContext ("");
+        var context = new OptionContext (null);
         context.set_translation_domain (GETTEXT_PACKAGE);
         context.add_group (Gtk.get_option_group (true));