Uno discard and draw pile empty?
There's always a card on the discard pile. Even when you reshuffle, you have to leave the top card of the former DISCARD pile as the start of the new DISCARD pile. (That is: you always have a card there showing what needs to be matched.)

Even if all the other cards are in players' hands, that card is still there. At this point, players can pass, but they draw nothing for doing so. Eventually someone will play.

If no one wants to play for whatever reason, then call it a draw: there's no point to playing when no one playing wants to play.