Optional annotation does not properly work for World

```
@Default
@CommandPermission("rtp.teleport.self")
@CommandCompletion("@players")
public void onTeleport(CommandSender sender, @Optional @CommandPermission("rtp.teleport.other") OnlinePlayer target, @Optional @CommandPermission("rtp.teleport.world") World world) {
Player player;
if (target == null && sender instanceof Player) {
player = (Player) sender;
} else {
player = target.getPlayer();
}
if (world == null) {
world = configHandler.getDefaultWorld();
}
final World finalWorld = world;

//Add it to the Scheduler to not falsely trigger the "Moved to quickly" warning
new BukkitRunnable() {
@Override
public void run() {
teleport(player, finalWorld, sender.hasPermission("rtp.teleport.bypass"));
}
}.runTaskLater(plugin, 1);
}
```