echars 环形图 无数据时，如何设置环的背景颜色

[Panda_Joy]

option = {
tooltip : {
trigger: 'item',
formatter: "{a} <br/>{b} : {c} ({d}%)"
},
legend: {
orient : 'vertical',
x : 'left',
data:['直接访问','邮件营销','联盟广告','视频广告','搜索引擎']
},
toolbox: {
show : true,
feature : {
mark : {show: true},
dataView : {show: true, readOnly: false},
magicType : {
show: true,
type: ['pie', 'funnel'],
option: {
funnel: {
x: '25%',
width: '50%',
funnelAlign: 'center',
max: 1548
}
}
},
restore : {show: true},
saveAsImage : {show: true}
}
},
calculable : true,
series : [
{
name:'访问来源',
type:'pie',
radius : ['60%', '80%'],
itemStyle : {
normal : {
label : {
show : false
},
labelLine : {
show : false
}
}

},
data:[
{value:0, name:'直接访问'},
{value:0, name:'邮件营销'},
{value:0, name:'联盟广告'},
{value:0, name:'视频广告'},
{value:0, name:'搜索引擎'}
]
}
]
};