--- includes/theme.inc	Sat Oct 17 05:10:31 2009 -0700
+++ includes/theme.inc	Sat Oct 17 18:44:20 2009 -0700
@@ -763,6 +763,7 @@ function theme($hook, $variables = array
 
   if (!isset($hooks[$hook])) {
     watchdog('theme', 'Theme key "@key" not found.', array('@key' => $hook), WATCHDOG_WARNING);
+    return '';
   }
 
   $info = $hooks[$hook];