return type can be null

frontend-js/src/main/js/map/data/PrivilegeType.js

@@ -50,7 +50,7 @@ PrivilegeType.prototype.setObjectType = function (objectType) {
 
 /**
  *
- * @returns {string}
+ * @returns {?null|string}
  */
 PrivilegeType.prototype.getObjectType = function () {
   return this._objectType;