@Override
    public ClusterStateBundle retrieveLastPublishedStateBundle() {
        Stat stat = new Stat();
        try {
            byte[] data = session.getData(paths.publishedStateBundle(), false, stat);
            lastKnownStateBundleZNodeVersion = stat.getVersion();
            if (data != null && data.length != 0) {
                EnvelopedClusterStateBundleCodec envelopedBundleCodec = new SlimeClusterStateBundleCodec();
                return envelopedBundleCodec.decodeWithEnvelope(data);
            }
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        } catch (Exception e) {
            maybeLogExceptionWarning(e, "Failed to retrieve last published cluster state bundle from " +
                    "ZooKeeper, will use an empty state as baseline");
        }
        // If we return a default, empty bundle, writes dependent on this bundle should only
        // succeed if the previous znode version is 0, i.e. not yet created.
        lastKnownStateBundleZNodeVersion = 0;
        return ClusterStateBundle.ofBaselineOnly(AnnotatedClusterState.emptyState());
    }
If this is called, we assume we're in shutdown situation, or we are doing it because we need a new session.
Thus we only need to free up resources, no need to notify anyone.
clustercontroller-core/src/main/java/com/yahoo/vespa/clustercontroller/core/database/ZooKeeperDatabase.java