I use SfCircularChart in my project. When I switch from light mode to dark mode or vise versa I have the exception:

Unexpected Null value

As you may see you compare point.startAngle! with oldStartAngle! but oldStartAngle is null. So we have a crash in the file /lib/src/circular_chart/renderer/renderer_extension.dart

I noticed that this crash is occurrend when I use my own legendItemBuilder. And moreover the prototype of legendItemBuilder is

legendItemBuilder: (legendText, series, point, seriesIndex) {
  print(series); // <--- returns `Instance of 'DoughnutSeriesRendererExtension'`
  return MyWidget();
}

I am confident the other value it should be printed.