private Map<String, MetricValue> getMap(Point point) {
        if (point == null) {
            point = Point.emptyPoint();
        }
        if (! perPointData.containsKey(point)) {
            perPointData.put(point, new HashMap<>());
        }
        return perPointData.get(point);
    }
Convert simple metrics snapshots into jdisc state snapshots.

@author arnej27959
container-core/src/main/java/com/yahoo/metrics/simple/jdisc/SnapshotConverter.java