为什么会出现这样的错误啊？

HTTP Status 500 - No input attribute for mapping path /userdd--------------------------------------------------------------------------------type Status reportmessage No input attribute for mapping path /userdddescription The server encountered an internal error (No input attribute for mapping path /userdd) that prevented it from fulfilling this request.服务器遇到一个内部错误（不映射路径/ userdd输入属性）无法实现这一要求的。