Windshield Washer Fluid - Tank Empty & No Cap - OOS Viol? CSA?

Bag + zip tie = instant cap

 

You neef need the washer to work. Dump a bit of fluid in to make sure it does and fashions a cap out of zip lock bag and zip tie or rubber band.

I'm on my phone so can't copy/paste well but here are the links.
eCFR — Code of Federal Regulations
Which references... 49 CFR 571.104 - Standard No. 104; Windshield wiping and washing systems.

 

If issued, then get the shop to fix.

 

Washer fluid reservoir caps can be had almost anywhere even off a older junk car many will fit

 

It can be. We had a driver at one place I worked get a ticket for defective windshield wipers. I suspect he used he couldn't see due to them as an excuse for something. Salt spray can be enough to block your vision but not enough to actually clean the windshield. I would certainly clean the windows every time you stop. You ought to buy some fluid and put it in there, many companies will authorize it on your fuel card and if no reimburse you. No cap likely won't get you in any trouble, but not being able to see certainly can and don't use it as an excuse.