@Override
    public V putIfAbsent(String key, V value) {
        return Map.super.putIfAbsent(key.toLowerCase(), value);
    }
@Test
    void putIfAbsent() {
        Map<String, Object> map = new LowerCaseLinkHashMap<>(lowerCaseLinkHashMap);
        Object obj = map.putIfAbsent("putIfAbsent", "putIfAbsent");
        Assertions.assertNull(obj);
        Assertions.assertEquals("putIfAbsent", map.get("putIfAbsent"));
        obj = map.putIfAbsent("key", "putIfAbsent");
        Assertions.assertEquals("Value", obj);
        Assertions.assertEquals("Value", map.get("key"));
    }