Hm, I'd say "don't teleport into black nothingness" should be common sense really. :) But you can reward players with an amusing death message at least if they still decide to do it.

Issue is random teleports, and also teleports out of line of sight. Somewhat of a problem, as teleportation is supposed to be required to beat the time limit. Also, teleporting to darkforge stairs which are turned into a patch of nothingness and dying is unnecessarily harsh.