Created attachment 55819 [details] [review]
I'm seeing a bunch of
(gnome-settings-daemon:13241): GLib-CRITICAL **: g_variant_new_string: assertion `string != NULL' failed
when starting gnome-settings-daemon
NULL is not a valid string, as far as GLib is concerned. Attaching a patch, but you should probably audit your gdbus port in general for NULL strings.
Committed, thanks. I've also fixed up two other places where this could be a problem and reviewed all of PkClient and PkControl.