anchor.diff:      return MaterialApp.router(
         title: 'Wishlist App',
         routerDelegate: BeamerRouterDelegate(
  -        locationBuilder: (state) => WishlistLocation(_appState, state),
  +        transitionDelegate: NoAnimationTransitionDelegate(),
  +        locationBuilder: (beamState) => WishlistLocation(_appState, beamState),
         ),
         routeInformationParser: BeamerRouteInformationParser(),
       );
  
positive.code:             key: ValueKey('wishlist-${state.pathParameters['wishlistId']}'),
              child: WishlistScreen(
                wishlist: _appState.wishlists.firstWhere(
                  (wishlist) => wishlist.id == state.pathParameters['wishlistId'],
                  orElse: () {
                    final wishlist =
                        Wishlist(state.pathParameters['wishlistId']!);
  
negative.code: }
  
  class WishlistLocation extends BeamLocation {
    WishlistLocation(AppState appState, BeamState beamState)
        : _appState = appState,
          super(beamState) {
      _appState.addListener(
        () => update((beamState) {
          var selectedWishlist = _appState.selectedWishlist;
          if (selectedWishlist != null) {
            return beamState.copyWith(
                pathBlueprintSegments: ['wishlist', ':wishlistId'],
                pathParameters: {'wishlistId': selectedWishlist.id});
          }
          return beamState
              .copyWith(pathBlueprintSegments: ['wishlist'], pathParameters: {});
        }),
      );
    }
  
    final AppState _appState;
  