关于Extjs柱状图的缓存问题

如下图：
当store里面没有数据时候，柱状图的里面还是显示有数据，显示的还是界面加载时的初始值，这个问题怎么解决？？？
柱状图的代码如下：
    var barChart = Ext.create('Ext.chart.Chart', {
        flex: 1,
        shadow: true,
        animate: true,
//        resizable:true,
        store: chartStore,
//        background: {
//            fill: 'rgb(17, 17, 17)'
//        },
        gradients: [
                    {
                        'id': 'v-1',
                        'angle': 0,
                        stops: {
                            0: {
                                color: 'rgb(212, 40, 40)'
                            },
                            100: {
                                color: 'rgb(117, 14, 14)'
                            }
                        }
                    },
                    {
                        'id': 'v-2',
                        'angle': 0,
                        stops: {
                            0: {
                                color: 'rgb(180, 216, 42)'
                            },
                            100: {
                                color: 'rgb(94, 114, 13)'
                            }
                        }
                    },
                    {
                        'id': 'v-3',
                        'angle': 0,
                        stops: {
                            0: {
                                color: 'rgb(43, 221, 115)'
                            },
                            100: {
                                color: 'rgb(14, 117, 56)'
                            }
                        }
                    },
                    {
                        'id': 'v-4',
                        'angle': 0,
                        stops: {
                            0: {
                                color: 'rgb(45, 117, 226)'
                            },
                            100: {
                                color: 'rgb(14, 56, 117)'
                            }
                        }
                    },
                    {
                        'id': 'v-5',
                        'angle': 0,
                        stops: {
                            0: {
                                color: 'rgb(187, 45, 222)'
                            },
                            100: {
                                color: 'rgb(85, 10, 103)'
                            }
                        }
                    }],
        axes:[{
            type:'Numeric',
            position:'left',//放置到左边
            fields:['count'],
            title:'指标值',
            grid: {
                odd: {
                    stroke: '#555'
                },
                even: {
                    stroke: '#555'
                }
            },
            grid:true,
            minimum:0,//可以看一下运行的效果是，y坐标是从0开始的
            //maximum :30,
        },{
                type:'Category',
                position:'bottom',
                fields:['serv_name'],
                title:'服务名称',
                grid: true,
                label: {
                 renderer: function(v) {
                        return Ext.String.ellipsis(v, 6, false);
                    },
                    rotate: {
                        degrees: 30
                    }
                }
        }],//轴
        series: [{
            type: 'column',
            axis: 'left',
            highlight: true,
            label: {
                display: 'insideEnd',
                'text-anchor': 'middle',
                  field: 'count',
                  orientation: 'horizontal',
                  fill: '#ffff',
                  font: '17px Arial'
              },
              renderer: function(sprite, storeItem, barAttr, i, store) {
                  barAttr.fill = colors[i % colors.length];
                  return barAttr;
              },
              style: {
                width:100,
                opacity: 0.95
              },
            xField: 'serv_name',
            yField: ['count'],
            tips:{//提示
                trackMouse:true,
                width:140,
                height:38,
                renderer:function(storeItem,item){
                    this.setTitle(storeItem.get('serv_name') + ':' +
                    storeItem.get('count') + '次');    
                }
        }
        }]        
    });Ext JS