help with plugin

If player stay on block (46) its block rebuild to id 0
Sorry for bad english

Somewhere in main class onEnable(): $this->getServer()->getScheduler()->scheduleRepeatingTask(new CheckBlockTask($this), 5);

PHP:

namespace your\own\name\space;
use pocketmine\block\Block;
use pocketmine\scheduler\PluginTask;
class CheckBlockTask extends PluginTask{
  public function onRun($t){
    foreach($this->getOwner()->getServer()->getOnlinePlayers() as $p){
      if($p->getLevel()->getBlock($v3 = $p->floor()->subtract(0, 1))->getId() === 46){
        $p->getLevel()->setBlock($v3, Block::get(0));
      }
    }
  }
}

Crush in public function onRun($t){

OK. Check $player->isOnline() first inside the foreach loop.