initialDatePickerMode property
Called when an enclosing form is saved. The value passed will be null
if format fails to parse the text.
Corresponds to the showDatePicker() parameter. Defaults to
DatePickerMode.day.
Implementation
// final FormFieldSetter<DateTime> onSaved;
/// Corresponds to the [showDatePicker()] parameter. Defaults to
/// [DatePickerMode.day].
final DatePickerMode initialDatePickerMode;