public void checkOutId(StockCus stockCus) {
        Optional.ofNullable(stockCus.getCusId()).ifPresent((b) -> {
            Optional<StockCus> byId = stockCusRepository.findById(b);
            Optional.ofNullable(byId).orElseThrow(() -> new BaseException("记录不存在"));
        });
        Optional.ofNullable(stockCus.getCusId()).ifPresent((b)->{
            Customer customer = customerService.get(b);
            Optional.ofNullable(customer).orElseThrow(()->new BaseException("记录不存在"));
        });

    }

            List<List<StockCus>> collect2 = stocks.stream().map(b -> b.getStockCusList()).collect(Collectors.toList());
            List<StockCus> collect3 = collect2.stream().flatMap(Collection::stream).collect(Collectors.toList());

        Map<Long, List<Stock>> collect1 = all1.stream().collect(Collectors.groupingBy(b -> b.getBrandId()));
//相同报错
Map<Long, User> maps = userList.stream().collect(Collectors.toMap(User::getId,Function.identity()));
//相同不报错
        Map<Long, User> maps = userList.stream().collect(Collectors.toMap(User::getId, Function.identity(), (key1, key2) -> key2));

   
Map<Long, String> maps = userList.stream().collect(Collectors.toMap(User::getId, User::getAge, (key1, key2) -> key2));

            Integer down = collect3.stream().filter(b -> b.getDownNum() != null).map(StockCus::getDownNum).reduce(Integer::sum).orElse(null);