Create a concept of a null item stack

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

@@ -7,7 +7,7 @@ public class CraftItemStack extends ItemStack {
     protected net.minecraft.server.ItemStack item;
 
     public CraftItemStack(net.minecraft.server.ItemStack item) {
-        super(item.c, item.a);
+        super(item != null ? item.c : 0, item != null ? item.a : 0);
         this.item = item;
     }
 
@@ -18,44 +18,68 @@ public class CraftItemStack extends ItemStack {
 
     @Override
     public Material getType() {
-        super.setTypeID(item.c); // sync, needed?
+        super.setTypeID(item != null ? item.c : 0); // sync, needed?
         return super.getType();
     }
 
     @Override
     public int getTypeID() {
-        super.setTypeID(item.c); // sync, needed?
-        return item.c;
+        super.setTypeID(item != null ? item.c : 0); // sync, needed?
+        return item != null ? item.c : 0;
     }
 
     @Override
     public void setTypeID(int type) {
-        super.setTypeID(item.c);
-        item.c = type;
+        if (type == 0) {
+            super.setTypeID(0);
+            super.setAmount(0);
+            item = null;
+        } else {
+            if (item == null) {
+                item = new net.minecraft.server.ItemStack(type);
+                super.setAmount(1);
+            } else {
+                item.c = type;
+                super.setTypeID(item.c);
+            }
+        }
     }
 
     @Override
     public int getAmount() {
-        super.setAmount(item.a); // sync, needed?
+        super.setAmount(item != null ? item.a : 0); // sync, needed?
         return item.a;
     }
 
     @Override
     public void setAmount(int amount) {
-        super.setAmount(amount);
-        item.a = amount;
+        if (amount == 0) {
+            super.setTypeID(0);
+            super.setAmount(0);
+            item = null;
+        } else {
+            super.setAmount(amount);
+            item.a = amount;
+        }
     }
 
     @Override
     public void setDamage(final byte damage) {
-        super.setDamage(damage);
-        item.d = damage;
+        // Ignore damage if item is null
+        if (item != null) {
+            super.setDamage(damage);
+            item.d = damage;
+        } 
     }
 
     @Override
     public byte getDamage() {
-        super.setDamage((byte) item.d); // sync, needed?
-        return (byte) item.d;
+        if (item != null) {
+            super.setDamage((byte) item.d); // sync, needed?    
+            return (byte) item.d;
+        } else {
+            return 0;
+        }
     }
 
 }