[Solved]-High Charts Line Chart with missing data-Highcharts

Highcharts draws a line only between two subsequent no-null points. Single points can be visualized as markers (which you disabled in your code).

Here's a live demo that shows this issue: http://jsfiddle.net/BlackLabel/khp0e8qr/

  series: [{
    data: [1, 2, null, 4, null, 1, 7],
    marker: {
        //enabled: false // uncomment to hide markers
    }
  }]

API reference: https://api.highcharts.com/highcharts/series.line.marker