echart 折线图 某个数据之后线变为虚线

let xLabel = [
  '1月',
  '2月',
  '3月',
  '4月',
  '5月',
  '6月',
  '7月',
  '8月',
  '9月',
  '10月',
  '11月',
  '12月'
];
let dataValue = [510, 465, 440, 570, 480, 615];
let dataValue1 = [
  ...new Array(dataValue.length - 1).fill('-'),
  dataValue[dataValue.length - 1],
  690,
  525,
  354,
  442,
  420,
  900
];
option = {
  tooltip: {
    trigger: 'axis'
  },
  legend: {
    show: true,
    itemWidth: 30,
    itemHeight: 10
  },
  xAxis: [
    {
      type: 'category',
      data: xLabel
    }
  ],
  yAxis: [
    {
      type: 'value'
    }
  ],
  series: [
    {
      name: '预测',
      type: 'line',
      symbol: 'none',
      smooth: true,
      data: dataValue
    },
    {
      name: '预测',
      type: 'line',
      symbol: 'none',
      smooth: true,
      itemStyle: {
        normal: {
          lineStyle: {
            type: 'dotted'
          }
        }
      },
      data: dataValue1
    }
  ]
};