如何在FusionCharts JS中构建多层饼图而无需填充？

// 创建数据源对象
var dataSource = {
  chart: {},
  data: [
    {
      id: "series1",
      label: "Series 1",
      value: 30
    },
    {
      id: "series2",
      label: "Series 2",
      value: 40
    },
    {
      id: "series3",
      label: "Series 3",
      value: 20
    }
  ]
};

// 创建配置对象
var chartConfig = {
  type: "multilevelpie",
  dataSource: dataSource
};

// 渲染图表
FusionCharts.ready(function() {
  var chart = new FusionCharts(chartConfig);
  chart.render("chart-container");
});