Presumably this happens if dbus-python doesn't manage to introspect the credentials interface, so it doesn't know how to marshal the empty dictionary.
I'm not sure why this would happen for some people and not others, but we could probably work around it by passing dbus.Dictionary({}, signature='ss') to find_credentials() instead (or whatever the signature is meant to be).
Presumably this happens if dbus-python doesn't manage to introspect the credentials interface, so it doesn't know how to marshal the empty dictionary.
I'm not sure why this would happen for some people and not others, but we could probably work around it by passing dbus.Dictionary({}, signature='ss') to find_credentials() instead (or whatever the signature is meant to be).