public Optional<VoterSet> valueAtOrBefore(long offset) {
        return votersHistory.valueAtOrBefore(offset);
    }
Computes the value of the voter set at a given offset.

This function will only return values provided through {@code addAt} and it would never
include the {@code staticVoterSet} provided through the constructor.

@param offset the offset (inclusive)
@return the voter set if one exist, otherwise {@code Optional.empty()}
raft/src/main/java/org/apache/kafka/raft/internals/VoterSetHistory.java