anchor.diff:  /// Service extensions can be found in [service_extensions.dart].
   class ServiceExtensionCheckbox extends _ServiceExtensionWidget {
     ServiceExtensionCheckbox({
  -    Key key,
  -    @required this.service,
  +    Key? key,
  +    required this.service,
     }) : super(
             key: key,
             // Don't show messages on success or when this toggle is in progress.
  
positive.code: /// Rich tooltip with a description and "more info" link
  class ServiceExtensionRichTooltip extends StatelessWidget {
    const ServiceExtensionRichTooltip({
      Key key,
      @required this.description,
      @required this.child,
    }) : super(key: key);
  
    final ToggleableServiceExtensionDescription description;
  
negative.code: /// a list of service extension checkbox settings.
  class ServiceExtensionCheckboxGroupButton extends StatefulWidget {
    ServiceExtensionCheckboxGroupButton({
      Key? key,
      required this.title,
      required this.icon,
      required this.extensions,
      required this.overlayDescription,
      this.tooltip,
      double overlayWidthBeforeScaling = _defaultWidth,
      this.minScreenWidthForTextBeforeScaling,
  