The getter 'sundayIsSelected' was called on null. Receiver: null Tried calling: sundayIsSelected

Question

here I created a model, and try to use the model in the page, but I get an error:

The getter 'sundayIsSelected' was called on null.
Receiver: null
Tried calling: sundayIsSelected

I set the sundayIsSelected in AlarmClock default value is false, why in the TimePickerPage there is still null? thanks!

Here is model code:

class AlarmClock {
  bool sundayIsSelected;

//I also tried followings:
//bool sundayIsSelected = false;

  AlarmClock({
    this.sundayIsSelected = false,
  });
}

here is my page code.

class TimePickerPage extends StatefulWidget {
  final AlarmClock alarmClock;

  const TimePickerPage({Key key, this.alarmClock}) : super(key: key);

  @override
  _TimePickerPageState createState() => _TimePickerPageState();
}

class _TimePickerPageState extends State<TimePickerPage> {

  bool sundayIsSelected;

@override
  void initState() {
    sundayIsSelected = widget.alarmClock.sundayIsSelected;
}
  Widget build(BuildContext context) {
    Text(sundayIsSelected),
 }
}