public class DemoBlockEntity extends BlockEntity implements ImplementedInventory {
    [...]
    @Override
    public void readNbt(NbtCompound nbt, RegistryWrapper.WrapperLookup registryLookup) {
        super.readNbt(nbt, registryLookup);
        Inventories.readNbt(nbt, items, registryLookup);
    }

    @Override
    public NbtCompound writeNbt(NbtCompound nbt, RegistryWrapper.WrapperLookup registryLookup) {
        Inventories.writeNbt(nbt, items, registryLookup);
        return super.writeNbt(nbt, registryLookup);
    }
}