function updatePollDescription(
        uint _idPoll, 
        bytes _description,
        uint8 _numBallots)
        public
    {
        require(_idPoll < _polls.length, "Invalid _idPoll");
        require(_numBallots <= 100, "Only a max of 100 ballots are allowed");

        Poll storage p = _polls[_idPoll];
        require(p.startBlock > block.number, "You cannot modify an active poll");
        require(p.author == msg.sender || msg.sender == controller, "Only the owner/controller can modify the poll");

        p.numBallots = _numBallots;
        p.description = _description;
        p.author = msg.sender;
    }