if a card effect shuffles up to x cards into that player's library and zero cards were choosen, would the player still have to shuffle his or her deck?
Depends I guess:
701.16c If an effect would cause a player to shuffle one or more specific objects into a library, but none of those objects are in the zone they’re expected to be in, that library isn’t shuffled. Example: Guile says, in part, “When Guile is put into a graveyard from anywhere, shuffle it into its owner’s library.” It’s put into a graveyard and its ability triggers, then a player exiles it from that graveyard in response. When the ability resolves, nothing happens. 701.16d If an effect would cause a player to shuffle one or more specific objects into a library, and a replacement or prevention effect causes all such objects to be moved to another zone instead, that library isn’t shuffled. Example: Black Sun’s Zenith says, in part, “Shuffle Black Sun’s Zenith into its owner’s library.” Black Sun’s Zenith is in a graveyard, has gained flashback (due to Recoup, perhaps), and is cast from that graveyard. Black Sun’s Zenith will be exiled, and its owner’s library won’t be shuffled. 701.16e If an effect would cause a player to shuffle a set of objects into a library, that library is shuffled even if there are no objects in that set. Example: Loaming Shaman says “When Loaming Shaman enters the battlefield, target player shuffles any number of target cards from his or her graveyard into his or her library.” It enters the battlefield, its ability triggers, and no cards are targeted. When the ability resolves, the targeted player will still have to shuffle his or her library.
Maybe you could specify the context, or a context?
Rules question? Have you read the Basic rulebook already? No? Why not take some time to do that?