You may cast Blessed Respite even if there are no cards in the target player's graveyard. If you do, they will still shuffle their library and combat damage will still be prevented.
18-06-2021
wotc
If you target yourself with Blessed Respite, it will not be shuffled into your library. It will go to your graveyard after it resolves.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.