Can I use Solving the riddle even though there aren't any rings left? For those who might ask why, I need to use it so that I can put the ring of void into play.
Solving the riddle without rings
A topic from AEG's L5R CCG Rules forum, copied for Oracle of the Void from a copy of the forum saved in October 2015, so pages it didn't save are missing. Players' names are left out; the rules officials are named. Rulings are as they stood on these dates; later rulings, the rulebooks and the Rules Archive may differ.
Can I use Solving the riddle even though there aren't any rings left?
Yes. http://rules.l5r.com/Abilities_and_acti ... Faith_Rule: "A player is not assumed to have complete knowledge of the face-down contents of his or her decks, for purposes of the Good Faith Rule."