如何使用Chartist js相对拉伸同一张图中具有不同索引数量的两个系列？

const trimNulls = (data) => {
  // Find the first non-null value
  const start = data.findIndex(y => y !== null);
  // Find the last non-null value
  const end = data.length - Array.from(data).reverse()
                                 .findIndex(y => y !== null);
  // Return the elements between those boundaries                               
  return data.slice(start, end);
}

const stretch = (data, newLength) => {
  // Create array of required number of nulls
  const stretched = Array(newLength).fill(null);
  // Determine the stretch factor
  const s = newLength / data.length;
  // For every value we want to keep, place it
  // at its new, stretched index
  data.forEach((y, x) => {
    stretched[Math.ceil(x * s)] = y;
  });
  // Return the newly created array
  return stretched;
}

// Takes a list of series and aligns their starts and ends, stretching 
// in between
const alignSeries = series => {
  // Trim each series
  const trimmed = series.map(trimNulls);
  // Find the longest one
  const maxLength = Math.max(...trimmed.map(t => t.length));
  // Stretch all series to the longest length and return
  return trimmed.map(t => stretch(t, maxLength));
};

var chart = new Chartist.Line('.ct-chart', {
  labels: [1, 2, 3, 4, 5, 6, 7],
  series: [
    ...alignSeries([
      [5, 5, 10, 8, 7, 5, 4],
      [10, 15, null, 12, null, null, null]
    ]),
    // For reference
    [10, 15, null, 12, null, null, null]
  ]
}, {
  lineSmooth: Chartist.Interpolation.cardinal({
    fillHoles: true,
  })
});

<script src="//cdn.jsdelivr.net/chartist.js/latest/chartist.min.js"></script>
<link href="//cdn.jsdelivr.net/chartist.js/latest/chartist.min.css" rel="stylesheet"/>
<div class="ct-chart"></div>