MyImmutableInventoryData

public class MyImmutableInventoryData extends AbstractImmutableData<MyImmutableInventoryData, MyInventoryData> {
        private Map<Integer, ItemStack> inventory;

        public MyImmutableInventoryData(Map<Integer, ItemStack> inventory) {
            this.inventory = inventory;
            registerGetters();
        }

        @Override
        protected void registerGetters() {
            registerFieldGetter(ToolKeys.INVENTORY, () -> this.inventory);
            registerKeyValue(ToolKeys.INVENTORY, this::inventory);
        }

        public ImmutableMapValue<Integer, ItemStack> inventory() {
            return Sponge.getRegistry().getValueFactory().createMapValue(ToolKeys.INVENTORY, inventory).asImmutable();
        }

        @Override
        public MyInventoryData asMutable() {
            return new MyInventoryData(inventory);
        }

        @Override
        public int getContentVersion() {
            return 1;
        }

        @Override
        public DataContainer toContainer() {
            return super.toContainer()
                    .set(ToolKeys.INVENTORY.getQuery(), this.inventory);
        }
    }