diff --git a/src/pocketmine/entity/Human.php b/src/pocketmine/entity/Human.php
index 8d4ed82c9..46f1e9106 100644
--- a/src/pocketmine/entity/Human.php
+++ b/src/pocketmine/entity/Human.php
@@ -485,7 +485,7 @@ class Human extends Creature implements ProjectileSource, InventoryHolder{
 			$slotCount = $this->inventory->getSize() + $this->inventory->getHotbarSize();
 			for($slot = $this->inventory->getHotbarSize(); $slot < $slotCount; ++$slot){
 				$item = $this->inventory->getItem($slot - 9);
-				if($item->getId() !== ItemItem::AIR){
+				if(!$item->isNull()){
 					$this->namedtag->Inventory[$slot] = $item->nbtSerialize($slot);
 				}
 			}
@@ -493,7 +493,7 @@ class Human extends Creature implements ProjectileSource, InventoryHolder{
 			//Armor
 			for($slot = 100; $slot < 104; ++$slot){
 				$item = $this->inventory->getItem($this->inventory->getSize() + $slot - 100);
-				if($item instanceof ItemItem and $item->getId() !== ItemItem::AIR){
+				if(!$item->isNull()){
 					$this->namedtag->Inventory[$slot] = $item->nbtSerialize($slot);
 				}
 			}
diff --git a/src/pocketmine/tile/Furnace.php b/src/pocketmine/tile/Furnace.php
index 31a5c5247..1aa8af256 100644
--- a/src/pocketmine/tile/Furnace.php
+++ b/src/pocketmine/tile/Furnace.php
@@ -216,7 +216,7 @@ class Furnace extends Spawnable implements InventoryHolder, Container, Nameable{
 		$raw = $this->inventory->getSmelting();
 		$product = $this->inventory->getResult();
 		$smelt = $this->server->getCraftingManager()->matchFurnaceRecipe($raw);
-		$canSmelt = ($smelt instanceof FurnaceRecipe and $raw->getCount() > 0 and (($smelt->getResult()->equals($product) and $product->getCount() < $product->getMaxStackSize()) or $product->getId() === Item::AIR));
+		$canSmelt = ($smelt instanceof FurnaceRecipe and $raw->getCount() > 0 and (($smelt->getResult()->equals($product) and $product->getCount() < $product->getMaxStackSize()) or $product->isNull()));
 
 		if($this->namedtag->BurnTime->getValue() <= 0 and $canSmelt and $fuel->getFuelTime() > 0 and $fuel->getCount() > 0){
 			$this->checkFuel($fuel);