function release() public {
    
    require((msg.sender == _sender) || (msg.sender == _beneficiary), "thou shall not pass!");
    require(block.timestamp >= _releaseTime, "not yet.");

    uint256 amount = _token.balanceOf(address(this));
    require(amount > 0, "zero balance");

    _token.safeTransfer(_beneficiary, amount);
  }