Mono usage for coordinator spring boot sample

mono_sample.java

public class OrderHandlers {
    private OrderService orderService;
    private KitchenService kitchenService;
    private DeliveryService deliveryService;
    private AccountingService accountingService;
    public OrderHandlers(OrderService orderService,
    KitchenService kitchenService,
    DeliveryService deliveryService,
    AccountingService accountingService) {
        this.orderService = orderService;
        this.kitchenService = kitchenService;
        this.deliveryService = deliveryService;
        this.accountingService = accountingService;
    }

    public Mono<ServerResponse> getOrderDetails(ServerRequest serverRequest) {
      String orderId = serverRequest.pathVariable("orderId");
      
      Mono<OrderInfo> orderInfo = orderService.findOrderById(orderId);
      
      Mono<Optional<TicketInfo>> ticketInfo =
      kitchenService
      .findTicketByOrderId(orderId)
      .map(Optional::of) 
      .onErrorReturn(Optional.empty()); 
      
      Mono<Optional<DeliveryInfo>> deliveryInfo =
      deliveryService
      .findDeliveryByOrderId(orderId)
      .map(Optional::of)
      .onErrorReturn(Optional.empty());
      
      Mono<Optional<BillInfo>> billInfo = accountingService
      .findBillByOrderId(orderId)
      .map(Optional::of)
      .onErrorReturn(Optional.empty());
      
      Mono<Tuple4<OrderInfo, Optional<TicketInfo>, 
      Optional<DeliveryInfo>, Optional<BillInfo>>> combined =
      
      Mono.when(orderInfo, ticketInfo, deliveryInfo, billInfo);
      
      Mono<OrderDetails> orderDetails = 
      combined.map(OrderDetails::makeOrderDetails);

      return orderDetails.flatMap(person -> ServerResponse.ok()
        .contentType(MediaType.APPLICATION_JSON)
        .body(fromObject(person)));
   }  
}