Balk with No Runners on Base?

With no runners on base, the pitcher is delivering from the set position. During his delivery, the pitcher fails to come to a complete stop.
 
The offensive team wants a balk called. The defensive coach argues that there cannot be a balk called without runners on base. In addition, he reminds the umpires the Mariano Rivera started each of his 652 saves from the set position without coming to a complete stop.
 
What do the umpires do now?
 
Call
In NF (and only NF), when the pitcher is delivering from the set position, he is required to come to a discernible stop, regardless of the number of base runners. If the pitcher does not stop, with no runners on base, this is an illegal pitch and a ball is awarded to the batter (NF 6-1-3).