diff -u b/core/modules/filter/filter.module b/core/modules/filter/filter.module
--- b/core/modules/filter/filter.module
+++ b/core/modules/filter/filter.module
@@ -65,7 +65,7 @@
       'variables' => array(
         'children' => NULL,
         'description' => NULL,
-        'attributes' => NULL,
+        'attributes' => array(),
       ),
       'template' => 'text-format-wrapper',
     ),