这是为何？？？

var west=new Ext.Panel({
    title: "功能菜单",
    width:200,
    region:"west",
    border:false,
    collapsible:true,
    layout:"accordion",
    layoutConfig:{
        animate:true
    },
    items:[{
        title:'菜单',
        collapsible:true,
        autoScroll:true,
        iconCls:"hotelmanageicon",
        items:[treenode]
    }]
});
去掉title:'菜单'就报错？？？