Fixed rare NPEs with CraftItemStack. This fixes BUKKIT-51

src/main/java/org/bukkit/craftbukkit/inventory/CraftItemStack.java

@@ -3,7 +3,6 @@ package org.bukkit.craftbukkit.inventory;
 import java.util.HashMap;
 import java.util.Map;
 import net.minecraft.server.EnchantmentManager;
-import net.minecraft.server.NBTBase;
 import net.minecraft.server.NBTTagCompound;
 import net.minecraft.server.NBTTagList;
 import org.bukkit.enchantments.Enchantment;
@@ -135,7 +134,7 @@ public class CraftItemStack extends ItemStack {
 
     @Override
     public int getMaxStackSize() {
-        return item.getItem().getMaxStackSize();
+        return (item == null) ? 0 : item.getItem().getMaxStackSize();
     }
 
     @Override
@@ -152,6 +151,7 @@ public class CraftItemStack extends ItemStack {
 
     @Override
     public int getEnchantmentLevel(Enchantment ench) {
+        if (item == null) return 0;
         return EnchantmentManager.getEnchantmentLevel(ench.getId(), item);
     }
 
@@ -168,7 +168,7 @@ public class CraftItemStack extends ItemStack {
     @Override
     public Map<Enchantment, Integer> getEnchantments() {
         Map<Enchantment, Integer> result = new HashMap<Enchantment, Integer>();
-        NBTTagList list = item.getEnchantments();
+        NBTTagList list = (item == null) ? null : item.getEnchantments();
 
         if (list == null) {
             return result;
@@ -185,6 +185,8 @@ public class CraftItemStack extends ItemStack {
     }
 
     private void rebuildEnchantments(Map<Enchantment, Integer> enchantments) {
+        if (item == null) return;
+
         NBTTagCompound tag = item.tag;
         NBTTagList list = new NBTTagList("ench");