show: Handle keys of any type, and set an error if key doesn't exist
show: Handle keys of any type, and set an error if key doesn't exist

Previously we were just handling strings, and silently doing nothing
if the key didn't exist, which is pretty broken.

sujitfulse/ostree,GNOME/ostree,sujitfulse/ostree,sujitfulse/ostree,leandrosansilva/ostree,gatispaeglis/ostree,GNOME/ostree,gatispaeglis/ostree,leandrosansilva/ostree,leandrosansilva/ostree,resin-io/ostree,leandrosansilva/ostree,GNOME/ostree,gatispaeglis/ostree,sujitfulse/ostree,sujitfulse/ostree,leandrosansilva/ostree,resin-io/ostree,resin-io/ostree,gatispaeglis/ostree,resin-io/ostree,resin-io/ostree,GNOME/ostree,gatispaeglis/ostree,GNOME/ostree,gatispaeglis/ostree