Extjs4---Uncaught TypeError: Cannot read property ‘items’ of undefined

The MVC Application Architecture(地址：http://www.sencha.com/learn/the-mvc-application-architecture/)时遇到了一个错误:

"Uncaught TypeError: Cannot read property ‘items’ of undefined"

找了很久才发现是因为没有在List.js中配置colums

完整代码下载：http://download.csdn.net/detail/lc448986375/4587647

需要添加colums的代码：

Ext.define('AM.view.user.List',{extend:'Ext.grid.Panel',alias:'widget.userlist',title:'All Users',store:'Users',columns:[         {header:'Name',dataIndex:'name'},         {header:'Email',dataIndex:'email'}]});