OOPS cause by security check on milestones with missing series_target

 I cannot see the Launchpad Registry's milestones page on edge (OOPS-1295EB222), and I believe the reason is because the 2.1.x milestones do not have a series.
    https://edge.launchpad.net/launchpad-registry/+milestones
    https://edge.launchpad.net/launchpad-registry/+milestone/2.1.11

But I note that I can see these same pages on on lpnet:
    https://launchpad.net/launchpad-registry/+milestones
    https://launchpad.net/launchpad-registry/+milestone/2.1.11

The breakage is caused by a change to give the release manager edit permission. The Milestone's series_target.driver is tested. This series_target should never be None, but it clearly is in the case of the 2.1.x milestones. See bug

The work-around is to update security.EditMilestoneByTargetOwnerOrAdmins to check that there is a series_target before accessing the driver.
        if (self.obj.series_target is not None
            and user.inTeam(self.obj.series_target.driver)):
            # The user is a release manager.
            # XXX sinzui 2009-07-18 bug=40978: The series_target should never
            # be None, but Milestones in the production DB are like this.
            return True