getNewVisitObject hook in plugin (no replies)

I am trying to create a function doing something when a new visit happens. If I use the newVisitorInformation hook, it records stuff but that is only when a new visitor comes for the first time, not when he returns (correct?). So, trying to use getNewVisitObject instead:

public function getNewVisitObject($notification) {

$visit =& $notification->getNotificationObject();
$raw_data = serialize($visit);
... record into DB...

Then when I read it from DB, it is "null".

In the Piwik source https://github.com/piwik/piwik/blob/1.0/core/Tracker.php#L237 , we have:

$visit = null;
Piwik_PostEvent('Tracker.getNewVisitObject', $visit);

- looks like it deliberately passes "null" to the hook. Why, and how can I get a visit's info?