Water supply tapped into a floor drain in the crawlspace?

[Chris Zimmerman]

I ran into this yesterday at brand new construction inspection. It is a smaller home on a crawlspace. The plumber installed a floor drain in the crawlspace (which i really liked seeing), but i noticed that he plumbed a water supply line to the drain. The supply was tapped off the cold side near an exterior frost proof faucet. Near the drain there was a check valve (obviously to prevent cross contamination) and also a 1/4 turn ball valve. When I opened and closed the valve nothing happened and there were no other valves upstream to cutoff supply. Does this mean that the supply line terminates at the floor drain itself? Thanks in advance for any info.

[Chris Zimmerman]

Actually just realized that it's a p trap primer. However no supply was at the drain. Is there a knockout or plug that should have been removed?