return previous;
    public Object set(int index, Object obj) {        int size = check(index);        ListElement el = getElement(index);        if (el == null) {            if (obj != null) {                create(index, obj);            }            return null;        } else {            Object result = ssn().get(el, m_element);            if (obj == null && el.getIndex().intValue() < size - 1) {                ssn().delete(el);            } else {                ssn().set(el, m_element, obj);            }            return result;        }    }