diff --git a/lib/Doctrine/Record/Filter.php b/lib/Doctrine/Record/Filter.php
index 913b84ad5..80d4548f6 100644
--- a/lib/Doctrine/Record/Filter.php
+++ b/lib/Doctrine/Record/Filter.php
@@ -37,6 +37,11 @@ class Doctrine_Record_Filter
      * @var Doctrine_Record $_record        the record object this filter belongs to
      */
     protected $_record;
+    /**
+     * @var Doctrine_Null $null             a Doctrine_Null object used for extremely fast
+     *                                      null value testing
+     */
+    private static $null;
     /**
      * constructor
      *