public Map<LoadBalancerId, LoadBalancer> readLoadBalancers(Predicate<LoadBalancerId> filter) {
        return readLoadBalancerIds(filter).stream()
                                          .map(this::readLoadBalancer)
                                          .filter(Optional::isPresent)
                                          .map(Optional::get)
                                          .collect(collectingAndThen(toLinkedMap(LoadBalancer::id,
                                                                                 Function.identity()),
                                                                     Collections::unmodifiableMap));
    }
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