Checkin a support function that is needed by the Transaction model since several checkins ago.

git-svn-id: file:///svn-source/pmgr/branches/surplus_account_20090815@590 97e9348a-65ac-dc4b-aefc-98561f571b83

site/app_model.php

@@ -402,6 +402,10 @@ class AppModel extends Model {
   }
 
 
+  function filter_null($array) {
+    return array_diff_key($array, array_filter($array, 'is_null'));
+  }
+
   function recursive_array_replace($find, $replace, &$data) {
     if (!isset($data))
       return;