getBlockIdAt Error

Hello guys I have to be able to clear all the blocks in 6 y
of endstone but I can not someone can help me out?

Error : Call to a member function getBlockIdAt() on null
Code:

PHP:

                                        $lv = $this->$arenas;
                                            for ($x = -999; $x <= 1000; $x++){
                                               for ($z = -999; $z <= 100; $z++){
                                                 if ($lv->getBlockIdAt($x,6,$z) == Block::END_STONE){
                                                  $lv->setBlock(new Vector3($x,$y,$z), Block::get(0));
                                                  $pl->sendMessage("debug");
                                                    }
                                                   }
                                                 }      

$lv is null. Check that variable and make sure it's a Level object.

can i load level?

And $this->$arenas looks weird to me

can we see your full code? we want help you
you should change $this->$arenas; to $this->arenas;

for getBlockIdAt, i give you one example :

PHP:

$player = $ev->getPlayer();
$direction = $player->getDirectionVector();
$x = $direction->getX();
$z = $direction->getZ();
$block = $player->getLevel()->getBlockIdAt($player->getX(), ($player->getY() - 0.1), $player->getZ());