Comment 4 for bug 1220028

Hm, ultimately this is happening because one of the changes in the code was to use the proper API functions for creating a view and changing its access (View::create() and $view->set_access()) rather than inserting directly into the database, when creating the Group Homepage template page. This causes a "viewaccess" notification to get sent to the root user.

And something in the handling of that viewaccess notification, is what causes this warning. Specifically, it looks like the problem is that the Group Homepage is a group of type "grouphomepage", but with NULL for its group column. That causes problems in the code that tries to fetch its group.

Additionally (and separately), there's that earlier notice, "[DBG] ab (lib/activity.php:224) profile_url called with no user id". THAT happens while it's trying to process the "Profile Page" template which belongs to the root user, and THAT has been present since 1.7 stable, so it is not a regression.