diff --git a/handlers/views_handler_argument_null.inc b/handlers/views_handler_argument_null.inc
index 5b42728..6c38e2b 100644
--- a/handlers/views_handler_argument_null.inc
+++ b/handlers/views_handler_argument_null.inc
@@ -14,6 +14,11 @@ class views_handler_argument_null extends views_handler_argument {
   function option_definition() {
     $options = parent::option_definition();
     $options['must_not_be'] = array('default' => FALSE, 'bool' => TRUE);
+    $options['exception'] = array(
+      'contains' => array(
+        'value' => array('default' => NULL),
+      ),
+    );
     return $options;
   }