To recapitulate my position on IRC: the other dbus.String calls aren't relevant. The problem here is that at the point when retrieving information from python-apt, aptdaemon doesn't convert it to the types it requires internally. Worrying about the other dbus.String calls would miss the point and would at best mask other bugs, possibly in ways that would cause data corruption rather than crashes.
To recapitulate my position on IRC: the other dbus.String calls aren't relevant. The problem here is that at the point when retrieving information from python-apt, aptdaemon doesn't convert it to the types it requires internally. Worrying about the other dbus.String calls would miss the point and would at best mask other bugs, possibly in ways that would cause data corruption rather than crashes.