Fix issue #5467. Delete the undefined value after setting the defaultValue.

lib/instance.js

@@ -55,6 +55,7 @@ var initValues = function(values, options) {
       for (key in defaults) {
         if (values[key] === undefined) {
           this.set(key, Utils.toDefaultValue(defaults[key]), defaultsOptions);
+          delete values[key];
         }
       }
     }