class ObjectMultistack {

    public void push(String keyName, ValueWrapper valueWrapper) {
        Objects.requireNonNull(keyName, "Key name cannot be null.");
        Objects.requireNonNull(valueWrapper, "Value wrapper cannot be null.");

        MultistackEntry next = map.get(keyName);

        map.put(keyName, new MultistackEntry(valueWrapper, next));
    }

    public  ObjectMultistack();

}