public List<Snapshot> readSnapshots(String hostname) {
        return read(snapshotsPath.append(hostname), (data) -> SnapshotSerializer.listFromSlime(SlimeUtils.jsonToSlime(data), systemAccount)).orElseGet(List::of);
    }
Returns the instant after which a firmware check is required, if any.
node-repository/src/main/java/com/yahoo/vespa/hosted/provision/persistence/CuratorDb.java