doing bug nomination in a distro context oopses

OOPS-1859H2826

Trying to do https://bugs.launchpad.net/ubuntu/+bug/712075/+nominate

  NotFound: Object: <lp.bugs.model.bugtask.NullBugTask object at 0x1fea6050>, name: '+nominate'

    Traceback (most recent call last):
  Module zope.publisher.publish, line 134, in publish
    result = publication.callObject(request, obj)
  Module canonical.launchpad.webapp.publication, line 486, in callObject
    return mapply(ob, request.getPositionalArguments(), request)
  Module zope.publisher.publish, line 109, in mapply
    return debug_call(obj, args)
   - __traceback_info__: <security proxied zope.browserpage.metaconfigure.SimpleViewClass from /srv/launchpad.net/production/launchpad-rev-12274/lib/lp/bugs/browser/../templates/bug-nominate-for-series.pt instance at 0x2b9989c73850>
  Module zope.publisher.publish, line 115, in debug_call
    return obj(*args)
  Module canonical.launchpad.webapp.publisher, line 297, in __call__
    self.initialize()
  Module lp.bugs.browser.bugnomination, line 71, in initialize
    raise NotFound(self.current_bugtask, '+nominate', self.request)
NotFound: Object: <lp.bugs.model.bugtask.NullBugTask object at 0x1fea6050>, name: '+nominate'

Looks like ubuntu/+bug is where we are getting NullBugTask lookups from, making that usie a real bug task if any such context is available might be appropriate. A direct fix is obviously possible too.