Does Hanabi allow empty clues?
This depends on which edition you are playing.

There are different editions published by different people, and the R &amp; R Games rulebook answers this clearly:


  Important: The player must clearly point to the cards which he is giving information about. (Thus saying "You have zero of something" is not allowed as you cannot point to anything.)


However, this rule did not exist in the original publishing, and the designer of the game actually specifically said it was allowed.


  As per the heading really - when giving info can you tell someone they have zero of a colour or value?
  
  
    The official answer by Antoine is "yes" and we also included this in our rules.
  


It seems that one of the reasons to disallow this is that with that clue as an option, it is possible to come up with a fool-proof convention where each different clue you can give has a known meaning... basically you can encode information into the clues.