defaultValues.scala

let NONE = "NONE"

func keyVoteByAddress(votingId: Int, address: String) = "voting_" + votingId + "_vote_" + address


@Callable(i)
func vote(id: Int) => {
	let voteKey = keyVoteByAddress(id, i.caller.toBase58String())
	let vote = getString(this, voteKey).valueOrElse(NONE)

	# alternative option

	let vote = match getString(this, voteKey){
    	case s: String => s
    	case _ => NONE
	}

	if (vote == NONE) then ...
	else ...
}