在Kendo-ui-angular2图表中，如何在值为null或零时隐藏标签

import { Component } from '@angular/core';

@Component({
  selector: 'app-chart',
  template: `
    <kendo-chart [seriesDefaults]="seriesDefaults">
      <kendo-chart-series>
        <kendo-chart-series-item [data]="data" type="line">
          <kendo-chart-series-item-labels [template]="labelTemplate"></kendo-chart-series-item-labels>
        </kendo-chart-series-item>
      </kendo-chart-series>
    </kendo-chart>
  `
})
export class ChartComponent {
  public data: any[] = [1, null, 0, 2, 3];
  
  public seriesDefaults: any = {
    labels: {
      visible: true,
      template: this.labelTemplate
    }
  };
  
  public labelTemplate: string = '#= value ? value : "" #';
}