As Ajani Goldmane isn’t a legal card in standard right now, Andy has committed a Game Rule Violation (and, consequently, Norbert has Failed to Maintain the Game State).
CR 201.3. If an effect instructs a player to name a card, the player must choose the name of a card that exists in the Oracle card reference (see rule 108.1) and is legal in the format of the game the player is playing.
Both players will receive warnings, and now we have to consider the fix. If little enough has happened between when Andy resolved the Pithing Needle and Norbert cast Ajani Steadfast, the Head Judge may authorize a rewind of the entire situation, to the point when Pithing Needle was entering the battlefield. If a rewind is not deemed possible, we turn to the first partial fix available for GRVs,
If a player made an illegal choice or failed to make a required choice for a permanent on the battlefield, that player makes a legal choice.
Andy will make this choice immediately, and the players should be instructed to play more carefully in the future.