Error: Type 'DiagnosticableMixin' not found. class DateTimePickerTheme with DiagnosticableMixin {

[qq543237999]

flutter_cupertino_date_picker-1.0.26+2/lib/src/date_picker_theme.dart:23:7: Error: The type 'DiagnosticableMixin' can't be mixed in.
class DateTimePickerTheme with DiagnosticableMixin {

[TheHussein]

It's obsolete, someone made a fork that works, add this to your pubspec.yaml instead

dependencies:
  flutter:
    sdk: flutter
  flutter_cupertino_date_picker:
    git:
      url: https://github.com/imshashank/flutter-cupertino-date-picker # Repo
      ref: master # Branch name