Help error Chest::getSize()

Error: "Call to undefined method pocketmine\tile\Chest::getSize()" (EXCEPTION) in "plugins/Sw/src/svile/sw/SWarena" at line 311

Code :

PHP:

private function refillChests()
    {
        $contents = $this->pg->getChestContents();
        foreach ($this->pg->getServer()->getLevelByName($this->world)->getTiles() as $tile) {
            if ($tile instanceof Chest) {
                //CLEARS CHESTS
                for ($i = 0; $i < $tile->getSize(); $i++) {  #Line: 311
                    $tile->getInventory()->setItem($i, Item::get(0));
                }
                //SET CONTENTS
                if (empty($contents))
                    $contents = $this->pg->getChestContents();
                foreach (array_shift($contents) as $key => $val) {
                    if($val[0] == Item::SPLASH_POTION) {
                        $item = new SplashPotion();
                        $r = mt_rand(1, 5);
                        if($r == 1){
                          $item = Item::get(438, 10, 1);
                        }
                        if($r == 2){
                          $item = Item::get(438, 15, 1);
                        }
                        if($r == 3){
                          $item = Item::get(438, 28, 1);
                        }
                        if($r == 4){
                          $item = Item::get(438, 25, 1);
                        }
                        if($r == 5){
                          $item = Item::get(438, 21, 1);
                        }
                    } else
                        $item = Item::get($val[0], 0, $val[1]);
                    $tile->getInventory()->setItem($key, $item);
                    }

                foreach (array_shift($contents) as $key => $val) {
                    if($val[0] == Item::WOOL) {
                        $item = new \pocketmine\item\IronSword();
                        $item->addEnchantment(Enchantment::getEnchantment(9)->setLevel(mt_rand(1, 2)));
                    } else
                        $item = Item::get($val[0], 0, $val[1]);
                        
                          if($item->getId() == Item::STONE_SWORD || $item->getId() == Item::IRON_SWORD || $item->getId() == Item::DIAMOND_SWORD){
                                $rand = mt_rand(1, 2);
                                $enchants = array(9, 10, 11, 12, 13, 14);
                                  if($rand == 1){
                                 $item->addEnchantment(Enchantment::getEnchantment($enchants[array_rand($enchants)])->setLevel(mt_rand(1, 2)));
                                 $tile->getInventory()->setItem($key, $item);
                               }else{
                                 $tile->getInventory()->setItem($key, $item);
                               }
                          }
                          if($item->getId() == Item::STONE_PICKAXE || $item->getId() == Item::IRON_PICKAXE || $item->getId() == Item::DIAMOND_PICKAXE || $item->getId() == Item::STONE_AXE || $item->getId() == Item::IRON_AXE || $item->getId() == Item::DIAMOND_AXE){
                                $rand = mt_rand(1, 2);
                                $enchants = array(15, 17);
                                  if($rand == 1){
                                 $item->addEnchantment(Enchantment::getEnchantment($enchants[array_rand($enchants)])->setLevel(mt_rand(1, 2)));
                                 $tile->getInventory()->setItem($key, $item);
                               }else{
                                 $tile->getInventory()->setItem($key, $item);
                               }
                          }
                          if($item->getId() == Item::CHAIN_HELMET || $item->getId() == Item::CHAIN_CHESTPLATE || $item->getId() == Item::CHAIN_LEGGINGS || $item->getId() == Item::CHAIN_BOOTS || $item->getId() == Item::IRON_HELMET || $item->getId() == Item::IRON_CHESTPLATE || $item->getId() == Item::IRON_LEGGINGS || $item->getId() == Item::IRON_BOOTS || $item->getId() == Item::DIAMOND_HELMET || $item->getId() == Item::DIAMOND_CHESTPLATE || $item->getId() == Item::DIAMOND_LEGGINGS || $item->getId() == Item::DIAMOND_BOOTS){
                                $rand = mt_rand(1, 2);
                                $enchants = array(0, 1, 4, 5);
                                  if($rand == 1){
                                 $item->addEnchantment(Enchantment::getEnchantment($enchants[array_rand($enchants)])->setLevel(mt_rand(1, 2)));
                                 $tile->getInventory()->setItem($key, $item);
                               }else{
                                 $tile->getInventory()->setItem($key, $item);
                               }
                          }
                          if($item->getId() == 261){
                                $rand = mt_rand(1, 2);
                                $enchants = array(19, 20, 21);
                                  if($rand == 1){
                                 $item->addEnchantment(Enchantment::getEnchantment($enchants[array_rand($enchants)])->setLevel(mt_rand(1, 2)));
                                 $tile->getInventory()->setItem($key, $item);
                               }else{
                                 $tile->getInventory()->setItem($key, $item);
                               }
                          }
                }
             }
        }
        unset($contents, $tile);
    }