[Frankfurt30] Plague Null

Part of a 30 deck collection for casual play (see https://boardgamegeek.com/thread/2224342/).

I wanted to use the fun Kitara virus package, but pairing them with Freedom Khumalo and/or the two virus breakers would have been too powerful/one-dimensional. So I've given the whole teeming virusy bunch into Null's capable hands, along with Gravedigger to put some pressure on the Corp.