Stackoverflow when deepclone an object with recursive references.

[zoyanhui]

java.lang.StackOverflowError happends when deepclone an object with recursive references.
e.g.:

@Test
    public void deepCopy() {
        Map<String, Object> map = new HashMap<>();
        map.put("a", 1);
        map.put("b", map);
        Cloner cloner = new Cloner();
        Object o = cloner.deepClone(map);
        System.out.println(o);
    }