Summary: TB3fe73412 timeline.py:189:setDuration:AttributeError: 'NoneType' object has no attribute 'duration'

Traceback (most recent call last):
  File "/usr/share/pitivi/python/pitivi/ui/mainwindow.py", line 626, in _undoCb
    self.app.action_log.undo()
  File "/usr/share/pitivi/python/pitivi/undo.py", line 165, in undo
    self._runStack(stack, stack.undo)
  File "/usr/share/pitivi/python/pitivi/undo.py", line 205, in _runStack
    run()
  File "/usr/share/pitivi/python/pitivi/undo.py", line 80, in undo
    self._runAction(self.done_actions, "undo")
  File "/usr/share/pitivi/python/pitivi/undo.py", line 72, in _runAction
    method()
  File "/usr/share/pitivi/python/pitivi/timeline/timeline_undo.py", line 116, in undo
    self.property_name.replace("-", "_"), self.old_value)
  File "/usr/share/pitivi/python/pitivi/timeline/timeline.py", line 189, in setDuration
    duration = min(duration, self.factory.duration -
AttributeError: 'NoneType' object has no attribute 'duration'

Local variables in innermost frame:
snap: False
duration: 9235545096
set_media_stop: True
self: <pitivi.timeline.timeline.TimelineObject object at 0x2bc2790>
