When I add date picker then show 'Non-nullable instance field 'selectedDate' must be initialized. ' error

When I add date picker then show ‘Non-nullable instance field ‘selectedDate’ must be initialized. ‘ error

DateTime selectedDate;

  

    void showDatePicker() {
        showCupertinoModalPopup(
            context: context,
            builder: (BuildContext builder) {
              return Container(
                height: MediaQuery.of(context).copyWith().size.height * 0.25,
                color: Colors.white,
                child: CupertinoDatePicker(
                  mode: CupertinoDatePickerMode.date,
                  onDateTimeChanged: (value) {
                    if (value != null && value != selectedDate)
                      setState(() {
                        selectedDate = value;
                      });
                  },
                  initialDateTime: DateTime.now(),
                  minimumYear: 2019,
                  maximumYear: 2021,
                ),
              );
            });
      }

widget

>Solution :

If you want init variable selectedDate later, use late:

late DateTime selectedDate;

or if you want to make selectedDate can have a null value then initiate it like this:

DateTime? selectedDate;

"?" after data type mean nullable.