private void putAllForCreate(Map<? extends K, ? extends V> m) {
        for (Iterator<? extends Map.Entry<? extends K, ? extends V>> i = m
                .entrySet().iterator(); i.hasNext();) {
            Map.Entry<? extends K, ? extends V> e = i.next();
            putForCreate(e.getKey(), e.getValue());
        }
    }
Look for preexisting entry for key. This will never happen for clone
or deserialize. It will only happen for construction if the input Map
is a sorted map whose ordering is inconsistent w/ equals.
src/main/java/com/alibaba/fastjson/util/AntiCollisionHashMap.java