anchor.diff:  
           final wasSelected = extensionState.isSelected;
   
  -        serviceManager.serviceExtensionManager.setServiceExtensionState(
  +        serviceManager.serviceExtensionManager!.setServiceExtensionState(
             extensionState.description.extension,
             enabled: !wasSelected,
             value: wasSelected
  
positive.code: /// Service extensions can be found in [service_extensions.dart].
  class _ServiceExtensionToggle extends _ServiceExtensionWidget {
    const _ServiceExtensionToggle({
      Key key,
      @required this.service,
      @required String Function(dynamic) describeError,
    }) : super(
            key: key,
            // Don't show messages on success or when this toggle is in progress.
  
negative.code:         });
        });
        // Track whether the extension is actually exposed by the VM.
        final listenable = serviceManager.serviceExtensionManager!
            .hasServiceExtension(extensionName);
        extension.isAvailable = listenable.value;
        addAutoDisposeListener(
  