Fix crash in conf/etc. with empty optional values

core/string_util.js

@@ -45,6 +45,10 @@ const SIMPLE_ELITE_MAP = {
 };
 
 function stylizeString(s, style) {
+    if (!s) {
+        return '';
+    }
+
     var len = s.length;
     var c;
     var i;