reward.js

if (_rewardAmount > 0) {
  // address 0 mean reward with ETH
  if (_rewardTokenAddress == address(0)){
    // reward with ETH
      msg.sender.transfer(_rewardAmount);
  } else {
    // reward token
    require(
      _rewardTokenAddress._safeTransfer(
        msg.sender,
        _rewardAmount
      ),
      "fn: forward(), msg: token transfer failed"
    );
  }
}