public BeanIndexer<K> addUnsortedIndex(String property) {
	Map<Object, Set<K>> holder = index.get(property);
	if (holder != null && !(holder instanceof NavigableMap<?, ?>)) {
	    return this;
	}
	if (holder != null) {
	    removeIndex(property);
	}
	holder = new HashMap<Object, Set<K>>();
	index.put(property, holder);
	indexBeans(property, elements);
	return this;
    }