x轴空值匹配存在问题echarts 折线配置项内容和展示

x轴有5个值，A,B,C,D,null,Echarts将null转换成了null字符串而非null导致series中的null无法正确的与x轴匹配

      options = [{
    legend: {},
    tooltip: {},
    xAxis: {
        type: 'category',
        data:['A','B','C','D',null]
    },
    yAxis: {},
    // Declare several bar series, each will be mapped
    // to a column of dataset.source by default.
    series: [
        {
            type:'line',
            data:[['A',1],['B',2],['D',3],['C',4],[null,5]],
            encode:{
                x:0,
                y:1
            }
        },
    ]
},
{
    legend: {},
    tooltip: {},
    xAxis: {
        type: 'category',
    //    data:['A','B','C','D',null]
    },
    yAxis: {},
    series: [
        {
            type:'line',
            data:[['A',1],['B',2],['D',3],['C',4],[null,5]],
            encode:{
                x:0,
                y:1
            }
        },
    ]
},
];