The cards says up to 2 cards, but you can't choose 0 cards. I tried using it for the cantrip without wanting to give a card and i couldn't finish unless i gave at least one card.
That's the only time you can choose 0 cards, from my experience. I tried to end a round with the cantrip once, and it wouldn't let me proceed until I transferred a card. I thought it would process like Leadership, but it requires at least one card.
