Does Warwick's 'when I attack' trigger go on the stack even when there are no damaged units on the opponent's battlefield, and can damage be added in response?

Ruling: Warwick's trigger always goes on the chain when he attacks because it doesn't target. Cards can be chained in response to damage units before his ability resolves.

Nuances:

• Abilities that target (like blue Teemo) don't go on the chain at all if there are no valid targets
• Abilities that don't target (like Warwick) always trigger and go on the chain regardless of board state
• This sequencing enables combos like Warwick with Flurry of Blades