Comment 12 for bug 252079

I'm using GNOME, I removed whole /var/cache/cups directory and restarted cups.

I noticed that there were some printers in cups with device URI "file:/dev/null" - seemed suspicious. They even stayed there after I removed /etc/cups/printers.conf. Also I couldn't remove them from cups WWW interface. It turned out they were in the cache all this time. Removing the cache solved my problem entirely.