code: public ServerBuilder serviceUnder(String pathPrefix, Service<HttpRequest, HttpResponse> service) {
          defaultVirtualHostBuilderUpdated();
          defaultVirtualHostBuilder.serviceUnder(pathPrefix, service);
          return this;
      }
docs: Binds the specified {@link Service} under the specified directory of the default {@link VirtualHost}.
  
  @throws IllegalStateException if the default {@link VirtualHost} has been set via
  {@link #defaultVirtualHost(VirtualHost)} already