pocketmine\Server::getPlayer PHP Method

    public function getPlayer($name)
    {
        $found = null;
        $name = strtolower($name);
        $delta = PHP_INT_MAX;
        foreach ($this->getOnlinePlayers() as $player) {
            if (stripos($player->getName(), $name) === 0) {
                $curDelta = strlen($player->getName()) - strlen($name);
                if ($curDelta < $delta) {
                    $found = $player;
                    $delta = $curDelta;
                }
                if ($curDelta === 0) {
                    break;
                }
            }
        }
        return $found;
    }

 public function onCompletion(Server $server)
 {
     $player = $server->getPlayer($this->player);
     if ($player instanceof Player && in_array($this->data, array(0, 1, 2))) {
         $server->getPluginManager()->getPlugin("RankUp")->executeRankUp($player, $this->data, $this->gotreward);
     }
 }