@Override
        public String toString() {
            return "ReplicaState(" +
                "replicaId=" + replicaId +
                ", replicaDirectoryId=" + replicaDirectoryId +
                ", logEndOffset=" + logEndOffset +
                ", lastFetchTimestamp=" + lastFetchTimestamp +
                ", lastCaughtUpTimestamp=" + lastCaughtUpTimestamp +
                ')';
        }
Return the last millisecond timestamp at which this replica was known to be
caught up with the leader.
@return The value of the lastCaughtUpTime if known, empty otherwise
clients/src/main/java/org/apache/kafka/clients/admin/QuorumInfo.java