dataSource property Null safety

List<T>? dataSource
final, inherited

A collection of data required for rendering the series.

If no data source is specified, empty chart will be rendered without series.

Defaults to null

Widget build(BuildContext context) {
   return Container(
       child: SfFunnelChart(
           series: FunnelSeries<ChartData, String>(
               dataSource: <ChartData>[
                  ChartData('USA', 10),
                  ChartData('China', 11),
                  ChartData('Russia', 9),
                  ChartData('Germany', 10),


final List<T>? dataSource;