Solved Inventory slot 6 stays null after being set!

Code:java

Inventory inv = Bukkit.createInventory(null, 9, "test inventory");
ItemStack is = new ItemStack(Material.WOODEN_DOOR);
inv.setItem(6, is);
getLogger().info("######## slot 6 is null? "+(inv.getItem(6) == null));

Code:

[01:40:20 INFO]: [TestPlugin] Enabling TestPlugin v0.0.0-SNAPSHOT
[01:40:20 INFO]: [TestPlugin] ######## slot 6 is null? true

Entire plugin source: https://github.com/LB--/TestPlugin

What in the world is happening here? Slots 0-5 work, why doesn't slot 6?? I'm using CB1.7.9-R0.2

 

You are looking for WOOD_DOOR.
The one you are using is the block form, and MC blocks it from inventories.

 

Oh, why is there then WOODEN_DOOR and WOODEN_DOOR_BLOCK? That's really confusing.

EDIT: D'oh, there is IRON_DOOR and IRON_DOOR_BLOCK but not WOODEN_DOOR_BLOCK.