Strategy strategy = new RegistryStrategy(registry);
Serializer serializer = new Persister(strategy);
registry.bind(User.class, UserConverter.class);
registry.bind(Room.class, RoomConverter.class);
registry.bind(PollType.class, PollTypeConverter.class);
if (list != null && list.size() > 0) {
registry.bind(list.get(0).getCreated().getClass(), DateConverter.class);
}
writeList(serializer, backup_dir, "roompolls.xml", "roompolls", list);