diff --git a/site/app_model.php b/site/app_model.php
index 65470ba..7eb7f10 100644
--- a/site/app_model.php
+++ b/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;