diff --git a/src/Common/View/Helper/SubMenu.php b/src/Common/View/Helper/SubMenu.php
index e34343e..a049d6b 100644
--- a/src/Common/View/Helper/SubMenu.php
+++ b/src/Common/View/Helper/SubMenu.php
@@ -82,7 +82,7 @@ public function __toString()
         $menu->setRenderInvisible($flag);
 
         if (!$active) {
-            return;
+            return '';
         }
 
         $container = $active['page'];