Some roles' quest message when returning the nemesis lair refer to
sensing the presence/aura/whatever of the quest artifact, but it might
not be there anymore. In reported case, the nemesis had picked it up
and later fled up the stairs to another level. Other situations are
possible; it's feasible for the hero to already have it. So provide
an alternate message, and some extra code to decide whether to use it.
Other anomalous messages, such as looking down on the dead body of a
nemesis who didn't leave a corpse, can still occur.
projects / nethack / commit