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'}
		]
	}
);