Ye Olde Double Cheste

So double chests are causing my plugin to crash, and I'm not entirely sure why.
Single chests work fine.
The plugin is relocating chests to a new world location, and crashes when the player attempts to access the contents of the relocated chest.

I have seen two solutions for this. The first was to add in CraftBukkit or Minecraft (I forget which) as a dependancy, and use, I think, IInventory? Some odd non-API call. The other, it looked like, was to deal with each of the chests individually, but I think there was something more complicated to it than that which I'm missing.

The blocks are being looped and handled one at a time. Single chests still report an inventory size of zero, and items are being placed in chests in a manner that looks compatible to how they're being taken out.
This is the code that stores the information temporarily before moving it to the new block:

Code:

Inventory inventory = null;
...
Chest chest = ((Chest)theBlock.getState());
inventory = chest.getInventory();
...
                for(int slot = 0; slot < inventory.getSize(); slot++) {
                    if(inventory.getItem(slot).getTypeId() != 0) {
                        complexBlock.setItem(slot, inventory.getItem(slot));
                        inventory.setItem(slot, new ItemStack(0));
                    }
                }

ComplexBlock is a custom type of block. The items variable in it is this:

Code:

private ItemStack[] items = new ItemStack[27];

And this is the code that restores that information to the blocks (inventory variable is declared as above):

Code:

               for(int slot = 0; slot < inventory.getSize(); slot++){
                    if(complexBlock.items[slot] != null && complexBlock.items[slot].getTypeId() != 0) {
                        inventory.setItem(slot, complexBlock.items[slot]);
                    }
                }   

Any help would be appreciated. Thanks.

 

ItemStack(0) crashes the client.
Set it to null instead.

Also, free slot is considered as null.

 

ItemStack(0) only appeared once in the code, I changed "new ItemStack(0)" to "null".

Edit: Fixed it. Hooray!