I’m inclined to recommend a trap for this drain but only want some input from you guys.
Yes, it needs a P-trap.
Did you give it a nice big smell ?
Your pic indicates its not being used and if so why put a P-trap on it why not just cap it, the P-trap will just go dry and your back where you started
Just because there is no washer in place doesn’t mean it won’t be used. Many homes are sold without washers and dryers in place.
I would explain the danger presented here and require a correction by a Certified Plumber.