httl取session值的问题?报错

@梁飞 你好，想跟你请教个问题：

用httl取session中的值 ${session.user.userName}

报错：

No such property userName in class java.lang.Object, because no such method getUserName() or method isUserName() or method userName() or filed userName.
Occur to offset: 13653, line: 375, column: 23, char: ., in: 
/index.httl
========================================
...					${session.user.userName}...
                      ^-here
========================================    

它自己不会强转吗？