public NodeList byIncreasingOsVersion() {
        return sortedBy(Comparator.comparing(node -> node.status()
                                                         .osVersion()
                                                         .current()
                                                         .orElse(Version.emptyVersion)));
    }
Returns a copy of this sorted by current OS version (lowest to highest)
node-repository/src/main/java/com/yahoo/vespa/hosted/provision/NodeList.java