Traceback (most recent call last):
  File "/usr/bin/update-manager", line 115, in <module>
    app.start_update()
  File "/usr/lib/python3/dist-packages/UpdateManager/UpdateManager.py", line 208, in start_update
    self.start_available()
  File "/usr/lib/python3/dist-packages/UpdateManager/UpdateManager.py", line 225, in start_available
    self._start_pane(pane)
  File "/usr/lib/python3/dist-packages/UpdateManager/UpdateManager.py", line 161, in _start_pane
    pane.start()
  File "/usr/lib/python3/dist-packages/UpdateManager/Dialogs.py", line 285, in start
    self.window_main.get_window().set_functions(Gdk.WMFunction.MOVE |
AttributeError: 'NoneType' object has no attribute 'set_functions'