Index: includes/menu.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/menu.inc,v
retrieving revision 1.307
diff -u -p -r1.307 menu.inc
--- includes/menu.inc	3 Dec 2008 14:38:59 -0000	1.307
+++ includes/menu.inc	18 Dec 2008 17:51:15 -0000
@@ -549,7 +549,7 @@ function _menu_item_localize(&$item, $ma
         $item['title'] = t($item['title'], menu_unserialize($item['title_arguments'], $map));
       }
     }
-    elseif (drupal_function_exists($callback)) {
+    elseif ($callback && drupal_function_exists($callback)) {
       if (empty($item['title_arguments'])) {
         $item['title'] = $callback($item['title']);
       }