anchor.diff:    Future<void> Function([List<String>]) rerunFunction;
   
     NonNullableFix(this.listener,
  -      {List<String> included = const [], this.preferredPort})
  +      {List<String> included = const [],
  +      this.preferredPort,
  +      this.enablePreview = true})
         : includedRoot =
               _getIncludedRoot(included, listener.server.resourceProvider) {
       reset();
  
positive.code:         migration, includedRoot, listener, instrumentationListener);
      await state.refresh();
  
      if (_server == null) {
        _server = HttpPreviewServer(state, rerun, preferredPort);
        _server.serveHttp();
        port = await _server.boundPort;
  
negative.code:   /// which all included paths share.
    final String includedRoot;
  
    /// Indicates whether the web preview of migration results should be launched.
    final bool enablePreview;
  
    /// The HTTP server that serves the preview tool.
    HttpPreviewServer _server;
  
  