default value in xssOption class

lib/util/xssOption.js

@@ -1,9 +1,19 @@
 class XssOption {
 
   constructor(config) {
-    this.isXssPrevented = config.isXssPrevented;
-    this.tagWhiteList = config.tagWhiteList;
-    this.attrWhiteList = config.attrWhiteList;
+    const recommendedXssWhiteList = require('../util/recommendedXssWhiteList');
+
+    if (config) {
+      this.isXssPrevented = config.isXssPrevented || true;
+      this.tagWhiteList = config.tagWhiteList || recommendedXssWhiteList.tags;
+      this.attrWhiteList = config.attrWhiteList || recommendedXssWhiteList.attrs;
+    }
+    else {
+      this.isXssPrevented = true;
+      this.tagWhiteList = recommendedXssWhiteList.tags;
+      this.attrWhiteList = recommendedXssWhiteList.attrs;
+    }
+
   }
 
 }