diff --git a/styles/bootstrap/application.js b/styles/bootstrap/application.js
index 0f1508b0f..7dfb584b5 100644
--- a/styles/bootstrap/application.js
+++ b/styles/bootstrap/application.js
@@ -5,8 +5,12 @@
  * (see https://forums.select2.org/t/propperly-escape-option-value-to-prevent-xss/788)
  */
 chzn_template_func =  function (state) {
-	var subtitle = $(state.element).data('subtitle');
-	var warning = $(state.element).data('warning');
+	var subtitle = '';
+	if($(state.element).data('subtitle'))
+		subtitle = $(state.element).data('subtitle')+''; /* make sure it is a string */
+	var warning = '';
+	if($(state.element).data('warning'))
+		warning = $(state.element).data('warning')+''; /* make sure it is a string */
 	var html = '<span>'+state.text.replace(/</g, '&lt;')+'';
 	if(subtitle)
 		html += '<br /><i>'+subtitle.replace(/</g, '&lt;')+'</i>';