@Override
    public String toString() {
        return String.format(
            "CandidateState(localId=%d, localDirectoryId=%s,epoch=%d, retries=%d, voteStates=%s, " +
            "highWatermark=%s, electionTimeoutMs=%d)",
            localId,
            localDirectoryId,
            epoch,
            retries,
            voteStates,
            highWatermark,
            electionTimeoutMs
        );
    }
Get the set of voters that have rejected our candidacy.

@return The set of rejecting voters
raft/src/main/java/org/apache/kafka/raft/CandidateState.java