Select an enemy follower on the field. Deal it 5 damage and, if there's a Passion follower on your field, draw a card.
QIf there are no selectable enemy followers on the field, and I have a Passion follower on my field, can I still play this spell to draw a card?
ANo, you can't. If a spell requires you to select a target, and there are no valid targets on the field, that spell cannot be played at all.