Map<String, BigDecimal> map = new HashMap<String, BigDecimal>();
        Function<String,BigDecimal> compute = key -> BigDecimal.TEN;
        map.put("1",BigDecimal.ONE);
        map.computeIfAbsent("1", compute);
        map.computeIfAbsent("2", compute);
        System.out.println(map);

        map.clear();
        map.put("1",null);
        map.computeIfAbsent("1", compute);
        map.computeIfAbsent("2", compute);
        System.out.println(map);

        map.clear();
        Function<String,BigDecimal> computeNul = key -> null;
        map.computeIfAbsent("1", computeNul);
        System.out.println(map);