Before the player has met an NPC (reproduced by running on a new save) you can go to the calendar in town and lookup NPCs you haven't met. The failing reference is in the player's friendship's here: https://github.com/Pathoschild/LookupAnything/blob/master/LookupAnything/Framework/Subjects/CharacterSubject.cs#L69-L72

I suggest that we render a You haven't met this NPC yet field now for this case. An alternative I suppose is to suggest schedules #4 / where you can meet the NPC.

Fixed in the upcoming 1.5 release via 5b65e21.