堆叠线图无法正常填充area区域的颜色echarts 折线配置项内容和展示

堆叠线图中设置其中一条线的step为true时，areaStyle填充错误

      option = {
    title: {
        text: '堆叠线图'
    },
    xAxis: {
        data: ['Sun', 'Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat']
    },
    yAxis: {},
    series: [{
        type: 'line',
        data:[220, 182, 491, 234, 290, 330, 310],
        stack: '总量',
        areaStyle: {},
        // smooth: true,
        step: true
    }, {
        type: 'line',
        data:[220, 482, 191, 234, 290, 330, 310],
        stack: '总量',
        areaStyle: {},
        // smooth: true
        // step: true
        
    }]
};