title: ngx-charts-line-chart failing with Cannot read property 'getColor' of undefined
body: <p>I'm setting up a simple example of the line chart and it fails with the getColor on undefined error. If I remove the [results] data, the chart displays but then fails on missing data. Not sure how to track this problem down?</p>
  
  <p>Using ngx-charts 12.0.1
  I copied the example code from <a href="https://github.com/marjan-georgiev/Angular-CLI-ngx-charts-Demo" rel="noreferrer">https://github.com/marjan-georgiev/Angular-CLI-ngx-charts-Demo</a> and then added a second chart to the home page shown in the example below.</p>
  
  <p>I've tried removing as many variables as possible to get results.</p>
  
  <p>Tag:</p>
  
  <pre><code>&lt;div style="height: 100px"&gt;
    &lt;ngx-charts-line-chart
      [view]="view"
      [results]="single"
      class="chart-container"
      [scheme]="colorScheme"
      [legend]="showLegend"
      [gradient]="gradient"
      [xAxis]="showXAxis"
      [yAxis]="showYAxis"
      [showXAxisLabel]="showXAxisLabel"
      [showYAxisLabel]="showYAxisLabel"
      [xAxisLabel]="xAxisLabel"
      [yAxisLabel]="yAxisLabel"
      (select)="onSelect($event)"
      (activate)="onActivate($event)"
      (deactivate)="onDeactivate($event)"
    &gt;
    &lt;/ngx-charts-line-chart&gt;
  &lt;/div&gt;
  
  component data:
  single: any[] = [
      {
        name: "Germany",
        value: 8940000
      },
      {
        name: "USA",
        value: 5000000
      },
      {
        name: "France",
        value: 7200000
      },
      {
        name: "Mars",
        value: 720000
      }
    ];
  
  
    colorScheme = {
      domain: ["#5AA454", "#A10A28", "#C7B42C", "#AAAAAA"]
    };
  
  Console Error with [results]: 
      ERROR TypeError: Cannot read property 'getColor' of undefined
      at Object.eval [as updateDirectives] (LineSeriesComponent.html:14)
  
  
  Console Error without [results]:
  The chart is build on the page and, of course, empty. The following
  error shows up when I click on any portion of the empty chart.
  
  Error: &lt;rect&gt; attribute x: Expected length, "NaN".  
      platform-browser:1973
  </code></pre>