[gnome-mines] Do not translate empty string

[Jiro Matsuzawa <jmatsuzawa src gnome org>]

commit 3af718372aff858b40a53dbbc5431cf7f47abab9
Author: Jiro Matsuzawa <jmatsuzawa gnome org>
Date:   Tue Mar 19 15:42:58 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=695997

 src/gnome-mines.vala |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/src/gnome-mines.vala b/src/gnome-mines.vala
index cc4528f..c302dea 100644
--- a/src/gnome-mines.vala
+++ b/src/gnome-mines.vala
@@ -956,7 +956,7 @@ public class Mines : Gtk.Application
         Intl.bind_textdomain_codeset (GETTEXT_PACKAGE, "UTF-8");
         Intl.textdomain (GETTEXT_PACKAGE);
 
-        var context = new OptionContext ("");
+        var context = new OptionContext (null);
         context.set_translation_domain (GETTEXT_PACKAGE);
         context.add_group (Gtk.get_option_group (true));