public NodeTimeseries add(NodeMetricSnapshot snapshot) {
        List<NodeMetricSnapshot> list = new ArrayList<>(snapshots);
        list.add(snapshot);
        return new NodeTimeseries(hostname(), list);
    }
Returns the last (newest) snapshot in this, or empty if there are none.
node-repository/src/main/java/com/yahoo/vespa/hosted/provision/autoscale/NodeTimeseries.java