if(!(sender instanceof Player)) return false;
Player player = (Player)sender;
if(command.getName() == "teleport") {
    if(args.length == 1) {
        List<Player> matches = getServer().matchPlayer(args[0])
        if(matches.size()>1) {
            player.teleport(matches.get(0));
        } else {
            if(matches.size()==0)
                player.sendMessage(args[0] + " could not be found.");
            else
                player.sendMessage("Too many matches for "+args[0]);
        }
    } else {
        player.sendMessage("Invalid command.");
    }
    return true;
}