public int leaderId() {
        if (!leaderId.isPresent())
            throw new IllegalStateException("Attempt to access nil leaderId");
        return leaderId.getAsInt();
    }
Return if the replica has voted for the given candidate.

A replica has voted for a candidate if all of the following are true:
1. the node's id and voted id match and
2. if the voted directory id is set, it matches the node's directory id

@param nodeKey the id and directory id of the replica
@return true when the arguments match, otherwise false
raft/src/main/java/org/apache/kafka/raft/ElectionState.java