Server crash cause of getPlayer()

Hey I'm again
I do not know why my Server crashed, i just used getPlayer()
Heres the error: Call to undefined method ForeverCMD\main::getPlayer()
Here is the code i think caused the error:

Code:

    public function onPlayerJoin(PlayerJoinEvent $event)
    {
        $join = $this->getConfig()->get("join");
        $player = $this->getPlayer()->getName();
        $event->setJoinMessage(str_replace("{name}",$player,$join));
    }
    public function onPlayerQuit(PlayerQuitEvent $event)
    {
        $quit = $this->getConfig()->get("leave");
        $player = $this->getPlayer()->getName();
        $event->setQuitMessage(str_replace("{name}",$player,$quit));
    }