There can be several reasons somebody doesn't have installed frequently needed plugins (see bug 154206). In such case libnullplugin's install-plugin dialog can be very annoying. A clever idea is needed to allow the user to disable this behaviour.
*** This bug has been marked as a duplicate of 83754 ***
PS: Deleting the libnullplugin.so file seems to work
Grr. Why didn't I figure this out? Too simple :)