总是报dom为空或不是对象

/**
 * 树状图
 */
Ext.chart.Chart.CHART_URL = 'extjs/resources/charts.swf'
//编码处理Ext.onReady(function(){ 
var fields = [{name:'data',type:'string'},{name:'visits',type:'int'},{name:'views',type:'int'}]
   var str ="";
   var cbo = new Ext.form.ComboBox({
mode : 'local',
editable : false,
store : new Ext.data.SimpleStore({
   data : [['性别', '性别'], ['学历', '学历'],['部门信息','部门信息']],
   fields : ['text', 'value']
}),
displayField : 'text',
valueField : 'value',
triggerAction : 'all',
name:'text',
//该属性是获取cbo中的value值
hiddenName:'value',
emptyText : '请选择系别'
});
url = "ERPProject/src/com.erp.action.cm/EmployeeDeptAction!getDeptSum.action";
var store = new Ext.data.Store({
url:url,//获取数据
     method:'POST', //提交方式
     remoteSort:true,
     reader:new Ext.data.JsonReader({ //json方式读取数据
     id:'data',
totalProperty : 'results',
root : 'items'
     },fields)
 
     });
    
//定义一个刷新按钮
var button = new Ext.Button({
text:'刷新',
iconCls:'refresh',
iconAlian:'right',
handler:function()
{
if(Ext.get("value").dom.value=="")
{
Ext.Ajax.request({
url:'ERPProject/src/com.erp.action.cm/EmployeeDeptAction!getDeptSum.action',
//获取到com中的值传入到Action中
params:{type:"部门信息"}

})

}
else
{
Ext.Ajax.request({
url:'ERPProject/src/com.erp.action.cm/EmployeeDeptAction!getDeptSum.action',
//获取到com中的值传入到Action中
params:{type:Ext.get("value").dom.value}
})
store.load();

}
}
})
//创建一个查看报表的button
var search = new Ext.Button( {
text : '查看报表',
iconCls : 'search-act',
handler:function()
{
Ext.Ajax.request({
url:'ERPProject/src/com.erp.action.cm/EmployeeDeptAction!getDeptSum.action',
//获取到com中的值传入到Action中
params:{type:Ext.get("value").dom.value}
})
store.load();
}

});
    
    
    
    var panel =  new Ext.Panel({
    
        iconCls:'chart',
        title: '员工信息报表',
        frame:true,
        width:500,
        height:300,
        layout:'fit',
tbar:[cbo,'-',button,'->',search ],
        items: {
            xtype: 'columnchart',
            store: store,
            url:'extjs/resources/charts.swf',
            xField: 'data',
            yAxis: new Ext.chart.NumericAxis({
                displayName: 'Visits',
                labelRenderer : Ext.util.Format.numberRenderer('0,0')
            }),
            tipRenderer : function(chart, record, index, series){
                if(series.yField == 'visits'){
                    return Ext.util.Format.number(record.data.visits, '0,0') + '  ' + record.data.name;
                }else{
                    return Ext.util.Format.number(record.data.views, '0,0') + ' 人  ' + record.data.name;
                }
            },
            chartStyle: {
                padding: 10,
                animationEnabled: true,
                font: {
                    name: 'Tahoma',
                    color: 0x444444,
                    size: 11
                },
                dataTip: {
                    padding: 5,
                    border: {
                        color: 0x99bbe8,
                        size:1
                    },
                    background: {
                        color: 0xDAE7F6,
                        alpha: .9
                    },
                    font: {
                        name: 'Tahoma',
                        color: 0x15428B,
                        size: 10,
                        bold: true
                    }
                },
                xAxis: {
                    color: 0x69aBc8,
                    majorTicks: {color: 0x69aBc8, length: 4},
                    minorTicks: {color: 0x69aBc8, length: 2},
                    majorGridLines: {size: 1, color: 0xeeeeee}
                },
                yAxis: {
                    color: 0x69aBc8,
                    majorTicks: {color: 0x69aBc8, length: 4},
                    minorTicks: {color: 0x69aBc8, length: 2},
                    majorGridLines: {size: 1, color: 0xdfe8f6}
                }
            },
            series: [{
                type: 'column',
                displayName: 'Page Views',
                yField: 'views',
                style: {
                    image:'bar.gif',
                    mode: 'stretch',
                    color:0x99BBE8
                }
            }]
        }
    });
    var win = new Ext.Window({
     title:'123',
     width:800,
     height:500,
     closeAction:'hide',
     items:[panel]
    })    //Ext.data.JsonStore读入数据之前的事件,store不需要在写baseParams,因为会覆盖掉.
    //(每次调用都载入此函数,'load'则第一次不调用外,其余都调用).   
   
    store.on('beforeload',function()
     {
    
      this.baseParams = {   
     type:Ext.get("value").dom.value   
    };        })
    //加载数据
   store.load(); 
    var btn  = Ext.get("EmpR");
    btn.on('click',function(){
     win.show();
    })
});