private void dupeInventory(Player p) {
        final Set<ItemStackSnapshot> set = new HashSet<>();
        Inventory inventory = p.getInventory();

        for (Inventory slot : inventory.slots()) {
            Optional<ItemStack> peek = slot.peek();
            if (peek.isPresent()) {
                InventoryTransactionResult offer = inventory.offer(peek.get().copy());
                if (offer.getType() == InventoryTransactionResult.Type.FAILURE) {
                    Collection<ItemStackSnapshot> rejectedItems = offer.getRejectedItems().;
                    if (!rejectedItems.isEmpty()) {
                        set.addAll(rejectedItems);
                    }
                }
            }
        }

        //drop item (method from the documentation)

    }