diff --git a/src/pocketmine/inventory/Inventory.php b/src/pocketmine/inventory/Inventory.php
index cb00e586c..fd56c7b71 100644
--- a/src/pocketmine/inventory/Inventory.php
+++ b/src/pocketmine/inventory/Inventory.php
@@ -28,6 +28,7 @@ use pocketmine\item\Item;
 use pocketmine\Player;
 
 interface Inventory{
+	const MAX_STACK = 64;
 
 	public function getSize();
 
@@ -150,4 +151,8 @@ interface Inventory{
 	 * @return InventoryHolder
 	 */
 	public function getHolder();
+
+	public function onOpen(Player $who);
+
+	public function onClose(Player $who);
 }
diff --git a/src/pocketmine/item/Item.php b/src/pocketmine/item/Item.php
index c781725bb..6bfe7a85f 100644
--- a/src/pocketmine/item/Item.php
+++ b/src/pocketmine/item/Item.php
@@ -475,8 +475,8 @@ class Item{
 	}
 
 	public function __construct($id, $meta = 0, $count = 1, $name = "Unknown"){
-		$this->id = (int) $id;
-		$this->meta = (int) $meta;
+		$this->id = $id & 0xffff;
+		$this->meta = $meta !== null ? $meta & 0xffff : null;
 		$this->count = (int) $count;
 		$this->name = $name;
 		if(!isset($this->block) and $this->id <= 0xff and isset(Block::$list[$this->id])){
@@ -522,7 +522,7 @@ class Item{
 	}
 
 	public function setDamage($meta){
-		$this->meta = $meta & 0xFFFF;
+		$this->meta = $meta !== null ? $meta & 0xFFFF : null;
 	}
 
 	final public function getMaxStackSize(){