diff --git a/js/search/search_form_criteria_enum.js b/js/search/search_form_criteria_enum.js
index 9f4cf765d..807470092 100644
--- a/js/search/search_form_criteria_enum.js
+++ b/js/search/search_form_criteria_enum.js
@@ -25,7 +25,7 @@ $(function()
 
 			// Null value
 			'null_value': {
-				'code': null,
+				'code': 'null',
 				'label': Dict.S('Enum:Undefined'),
 			},