Hi Brian,
I for one think that you are right, and this mechanism is a little lacking. I found that need myself a short while back.
Let me offer this suggestion, which I used:
1) Use the no-op (Providing you work with 2.0) to find the volume, or know it is not there.
2) If the volume was not found, feed parameters to the repeat row finder that would ascertain NOTHING would be found,
and thus the row would be skipped.
Presuming that the volume is found into "vol1" you can write in the volume name parameter of the row finder:
vol1._found ? vol1.name : "NEVER_FIND_THIS"
This would work, as it did for another customer of mine (The customer wanted to resize a trio of volumes,
original, secondary and tertiary. Obviously, sometimes there's no secondary, and thus no tertiary....)
Hope that helps.
Best,
Yaron