    function _move(
        address operator,
        address from,
        address to,
        uint256 amount,
        bytes memory userData,
        bytes memory operatorData
    )
        private
    {
        _balances[from] = _balances[from].sub(amount);
        _balances[to] = _balances[to].add(amount);
        emit Sent(operator, from, to, amount, userData, operatorData);
        emit Transfer(from, to, amount);
    }