private Inventory getFuelInventory(Player player) { if (isValidFuelJacket(player.getInventory().getChestplate())) { FileConfiguration fuelConfig = getFuelConfig(player); Material jacket = player.getInventory().getChestplate().getType(); int jacketSize = getFuelJacketSize(jacket); String jacketType = getFuelJacketConfigString(jacket); if (fuelConfig.get(jacketType) != null) { Inventory fuelInventory; ArrayList<ItemStack> itemStack = new ArrayList<>(); itemStack.addAll( fuelConfig .getList(jacketType) .stream() .map(fuelCurrentItem -> (ItemStack) fuelCurrentItem) .collect(Collectors.toList())); fuelInventory = Bukkit.createInventory( player, jacketSize, "" + ChatColor.DARK_RED + ChatColor.BOLD + "Rocket Boot Fuel Jacket"); fuelInventory.setContents(itemStack.toArray(new ItemStack[itemStack.size()])); return fuelInventory; } } return null; }