@Override
    public String toString() {
        return "ZkMigrationLeadershipState{" +
            "kraftControllerId=" + kraftControllerId +
            ", kraftControllerEpoch=" + kraftControllerEpoch +
            ", kraftMetadataOffset=" + kraftMetadataOffset +
            ", kraftMetadataEpoch=" + kraftMetadataEpoch +
            ", lastUpdatedTimeMs=" + lastUpdatedTimeMs +
            ", migrationZkVersion=" + migrationZkVersion +
            ", controllerZkEpoch=" + zkControllerEpoch +
            ", controllerZkVersion=" + zkControllerEpochZkVersion +
            '}';
    }
A Kafka-internal constant used to indicate that the znode version is unknown. See ZkVersion.UnknownVersion.
metadata/src/main/java/org/apache/kafka/metadata/migration/ZkMigrationLeadershipState.java