If a player must Draw cards in excess to the number of cards in their deck, they will Draw as many as possible, perform this action, then Draw the remaining amount instructed.
§ 431.1.a Core Rules PDF (officieel)
§ 431 Burn Out
§ 431.1 Burning Out is an action a player must perform if they attempt to move one or more cards from their Main Deck to any other zone in excess of the number of cards remaining in their Main Deck: