public VirtualHostBuilder build(Function<? super HttpService, ? extends HttpService> decorator) {
        requireNonNull(decorator, "decorator");
        buildRouteList().forEach(route -> virtualHostBuilder.addRouteDecoratingService(
                new RouteDecoratingService(route, "/", decorator)));
        return virtualHostBuilder;
    }
Sets the {@code decorator} and returns {@link VirtualHostBuilder} that this
{@link VirtualHostDecoratingServiceBindingBuilder} was created from.

@param decorator the {@link Function} that decorates {@link HttpService}
core/src/main/java/com/linecorp/armeria/server/VirtualHostDecoratingServiceBindingBuilder.java