private IItemHandler inventory = new ItemStackHandler(6);

    @Override
    public boolean hasCapability(Capability<?> capability, EnumFacing facing){
        return capability == CapabilityItemHandler.ITEM_HANDLER_CAPABILITY || super.hasCapability(capability, facing);
    }

    @Override
    @Nullable
    public <T> T getCapability(Capability<T> capability, @Nullable EnumFacing facing){
        return capability == CapabilityItemHandler.ITEM_HANDLER_CAPABILITY ? (T)inventory : super.getCapability(capability, facing);
    }