function addWhiteListedInvestor(address _investor, string _referralCode) public
  {
    require(block.timestamp <= whiteListRegistrationEndTime);
    require(_investor != 0);
    require(!isWhiteListed[_investor]);
    bytes32 referralCodeHash = keccak256(_referralCode);
    require(referralCodes[referralCodeHash] == 0x0);
    
    isWhiteListed[_investor] = true;
    referralCodes[referralCodeHash] = _investor;
    WhiteListedInvestorAdded(_investor, _referralCode);
  }