WebWork 404页面未找到

   把webwork-2.2.2.jar升级到webwork-2.2.4.jar和xwork-1.1.3.jar升级到xwork-1.2.1.jar为什么会出现404的错误，而且控制台抛出 WARN [http-8080-Processor25] VisitorFieldValidator.warn(104) | The visited object is null, VisitorValidator will not be able to handle validation properly. Please make sure the visited object is not null for VisitorValidator to function properly         

  请指教，谢谢！