Crash on startup because of bad preferences

I get this crash on startup on Linux:

Traceback (most recent call last):
  File "run.py", line 62, in <module>
    sys.exit(main(sys.argv))
  File "run.py", line 50, in main
    mgapp =  MoneyGuru()
  File "/home/hsoft/src/moneyguru/qt/app.py", line 38, in __init__
    self.prefs.load()
  File "/home/hsoft/src/moneyguru/qtlib/preferences.py", line 84, in load
    self._load_values(self._settings)
  File "/home/hsoft/src/moneyguru/qt/preferences.py", line 20, in _load_values
    self.recentDocuments = list(filter(op.exists, self.recentDocuments))
TypeError: 'NoneType' object is not iterable

This is because, somehow, a bad pref snuck into my config file:

RecentDocuments=@Invalid()