R2-D2 Crew - what if you are damaged but have no facedown cards?

[jwfour]

If you have R2-D2 Crew (Rebels) and are damaged but have face-up damage cards, can you still use his ability to regain a shield, given that it would be impossible (if you roll a hit) to expose one of the damage cards?

I'm guessing the answer is no, because you are unable to pay the cost (flipping a card), but I wasn't sure.

[Dee Y]

R2-D2 (Rebel crew): "During the End Phase, if you are damaged and not shielded, you may roll 1 attack die to recover 1 shield. On a hit result, expose 1 of your damage cards."

"A ship can pay a cost for an effect only if the effect can be resolved."

 

Exposing a damage card with R2-D2 is an effect of the ability, not a cost.  You may use R2-D2 as long as you meet the requirements.  If you only have face up damage cards, and R2-D2 rolls a hit, that portion of his ability does not have any effect.