Getting item details from config?

I'm trying to make a GUI with customizable items in slots, it isn't really working.
When running the command, this code runs to generate the GUI:

Code:

    public void openGui(Player player) {
        for(int x = 0; x < 27; x++) {
            player.sendMessage(""+(short) config.getInt(x+".ItemData"));
            if(config.getConfigurationSection("Items.maingui").contains(String.valueOf(x))) {
                mainItems = new ItemStack(Material.getMaterial(config.getString(x+".Material")),
                        1,
                        (short) config.getInt(x+".ItemData"));
                createDisplay(mainItems, mainGui, x, config.getString(x+".Name"), config.getStringList(x+".Lore"));
            }
        }
        player.openInventory(mainGui);
    }

The createDisplay method is from a tutorial.
Apparently line 94: (short) config.getInt(x+".ItemData")); is a null pointer exception, despite it existing
Here is my config file:

Code:

GuiTitle: '&6&lJobs GUI'
AdminGuiTitle: '&c&lJobs Admin GUI'
Items:
  maingui:
    2:
      Material: DIAMOND_SWORD
      ItemData: 0
      Name: '&3&lDiamond Sword'
      Lore:
         - 'This is a sword!'
         - 'Change me!'

Any help?

EDIT: FIXED
I did a silly and only applied @timtower 's advice to the item data. Silly me

 

Full path to what, and where?
EDIT: Oh, I see what you mean. Thanks
EDIT2: @timtower I'm using this now and it still isn't working :/
(short) config.getInt("Items.maingui." + x + ".ItemData"))
EDIT3:
I've found the problem. It for some reason thinks that "ItemData: 0" in the config is a string, and so it can't find the number part. I tried getting the string and using Short.parseShort but it didn't work.
Any ideas?

 

@TheMinecraftKnight
If your problem has been solved, mark this thread as solved.