How to get an area and move it 1 block ahead on player move event

I have this code:

PHP:

  public function getPos1() {
      $this->pos1 = new Vector3($pos1["44"],$pos1["122"],$pos1["-896"]);
      return array($this->pos1->getX(),$this->pos1->getY(),$this->pos1->getZ());
  }
 
  public function getPos2() {
      $this->pos2 = new Vector3($pos2["44"],$pos2["125"],$pos2["-892"]);
      return array($this->pos2->getX(),$this->pos2->getY(),$this->pos2->getZ());
  }
 
  public function getBlocks(){
      $this->blocks = [];
      if((min($this->pos1->getX(),$this->pos2->getX()) <= $pos->getX()) && (max($this->pos1->getX(),$this->pos2->getX()) >= $pos->getX()) && (min($this->pos1->getY(),$this->pos2->getY()) <= $pos->getY()) && (max($this->pos1->getY(),$this->pos2->getY()) >= $pos->getY()) && (min($this->pos1->getZ(),$this->pos2->getZ()) <= $pos->getZ()) && (max($this->pos1->getZ(),$this->pos2->getZ()) >= $pos->getZ()) && ($this->level == $level)) {
          return array($this->blocks());
      }
  }
 
  public function checkVoid(PlayerMoveEvent $event){
      $level = $this->getServer()->getDefaultLevel();
      if($event->getTo()->getFloorY() > 122){;
        $b = $this->blocks;
        $X = $b->getX();
        $Y = $b->getY();
        $Z = $b->getZ();
        $pos = new Vector3($X-1, $Y, $Z);
        $level->setBlock($pos, $b, false, false);
        return;
      }
  }
}

What I'm trying to do here is get an area and move it X-1 (1 block ahead of itself) when a player moves above the height of Y 122 I'm currently getting this error:

Code:

[23:07:53] [Server thread/CRITICAL]: Could not pass event 'pocketmine\event\player\PlayerMoveEvent' to 'DeathView v0.0.2': Undefined property: TheDiamondYT\DeathView\Loader::$blocks on TheDiamondYT\DeathView\Loader
[23:07:53] [Server thread/CRITICAL]: ErrorException: "Undefined property: TheDiamondYT\DeathView\Loader::$blocks" (EXCEPTION) in "DeathView-master/src/TheDiamondYT/DeathView/Loader" at line 157
[23:07:53] [Server thread/DEBUG]: #0 DeathView-master/src/TheDiamondYT/DeathView/Loader(157): pocketmine\error_handler(integer 8, string Undefined property: TheDiamondYT\DeathView\Loader::$blocks, string C:\Users\Admin\Creative Cloud Files\Desktop\Lobby - DEV\plugins\DeathView-master\src\TheDiamondYT\DeathView\Loader.php, integer 157, array Array())
[23:07:53] [Server thread/DEBUG]: #1 src/pocketmine/plugin/MethodEventExecutor(38): TheDiamondYT\DeathView\Loader->checkVoid(pocketmine\event\player\PlayerMoveEvent object)
[23:07:53] [Server thread/DEBUG]: #2 src/pocketmine/plugin/RegisteredListener(98): pocketmine\plugin\MethodEventExecutor->execute(TheDiamondYT\DeathView\Loader object, pocketmine\event\player\PlayerMoveEvent object)
[23:07:53] [Server thread/DEBUG]: #3 src/pocketmine/plugin/PluginManager(721): pocketmine\plugin\RegisteredListener->callEvent(pocketmine\event\player\PlayerMoveEvent object)
[23:07:53] [Server thread/DEBUG]: #4 src/pocketmine/Player(1552): pocketmine\plugin\PluginManager->callEvent(pocketmine\event\player\PlayerMoveEvent object)
[23:07:53] [Server thread/DEBUG]: #5 src/pocketmine/Player(1662): pocketmine\Player->processMovement(integer 1)
[23:07:53] [Server thread/DEBUG]: #6 src/pocketmine/level/Level(751): pocketmine\Player->onUpdate(integer 1132)
[23:07:53] [Server thread/DEBUG]: #7 src/pocketmine/Server(2377): pocketmine\level\Level->doTick(integer 1132)
[23:07:53] [Server thread/DEBUG]: #8 src/pocketmine/Server(2534): pocketmine\Server->checkTickUpdates(integer 1132, double 1515847073.9604)
[23:07:53] [Server thread/DEBUG]: #9 src/pocketmine/Server(2274): pocketmine\Server->tick()
[23:07:53] [Server thread/DEBUG]: #10 src/pocketmine/Server(2149): pocketmine\Server->tickProcessor()
[23:07:53] [Server thread/DEBUG]: #11 src/pocketmine/Server(1737): pocketmine\Server->start()
[23:07:53] [Server thread/DEBUG]: #12 src/pocketmine/PocketMine(554): pocketmine\Server->__construct(BaseClassLoader object, pocketmine\utils\MainLogger object, string C:\Users\Admin\Creative Cloud Files\Desktop\Lobby - DEV\, string C:\Users\Admin\Creative Cloud Files\Desktop\Lobby - DEV\plugins\)
[23:07:53] [Server thread/DEBUG]: #13 C:/Users/Admin/Creative Cloud Files/Desktop/Lobby - DEV/PocketMine-MP.phar(1): require(string phar://C:/Users/Admin/Creative Cloud Files/Desktop/Lobby - DEV/PocketMine-MP.phar/src/pocketmine/PocketMine.php)

can someone help, there seems to be a problem with $blocks but I don't understand why when it's $this->blocks