Update manager failure

  File "/usr/lib/python3/dist-packages/UpdateManager/backend/InstallBackendAptdaemon.py", line 236, in _on_finished
    self._action_done(action,
  File "/usr/lib/python3/dist-packages/UpdateManager/backend/__init__.py", line 269, in _action_done
    self.window_main.start_available(is_cancelled_update)
  File "/usr/lib/python3/dist-packages/UpdateManager/UpdateManager.py", line 236, in start_available
    self.refresh_cache()
  File "/usr/lib/python3/dist-packages/UpdateManager/UpdateManager.py", line 397, in refresh_cache
    self.update_list.update(self.cache, eventloop_callback=iterate,
  File "/usr/lib/python3/dist-packages/UpdateManager/Core/UpdateList.py", line 521, in update
    if (pkg.name in duplicate_packages):
TypeError: argument of type 'NoneType' is not iterable

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/UpdateManager/backend/InstallBackendAptdaemon.py", line 244, in _on_finished
    self._action_done(action,
  File "/usr/lib/python3/dist-packages/UpdateManager/backend/__init__.py", line 269, in _action_done
    self.window_main.start_available(is_cancelled_update)
  File "/usr/lib/python3/dist-packages/UpdateManager/UpdateManager.py", line 236, in start_available
    self.refresh_cache()
  File "/usr/lib/python3/dist-packages/UpdateManager/UpdateManager.py", line 397, in refresh_cache
    self.update_list.update(self.cache, eventloop_callback=iterate,
  File "/usr/lib/python3/dist-packages/UpdateManager/Core/UpdateList.py", line 521, in update
    if (pkg.name in duplicate_packages):
TypeError: argument of type 'NoneType' is not iterable
^CTraceback (most recent call last):
  File "/usr/bin/update-manager", line 119, in <module>
    Gtk.main()
  File "/usr/lib/python3/dist-packages/gi/overrides/Gtk.py", line 1632, in main
    return _Gtk_main(*args, **kwargs)
  File "/usr/lib/python3.8/contextlib.py", line 120, in __exit__
    next(self.gen)
  File "/usr/lib/python3/dist-packages/gi/_ossighelper.py", line 251, in register_sigint_fallback
    signal.default_int_handler(signal.SIGINT, None)