place down a civilian player (or any other unit without a vest) in the editor and preview.
Then after the world starts, press escape, then put the following line of code into the debug console and click on Local Execute:
player addVest "V_ChestrigB_rgr"
Observe that nothing is put into your vest slot.

Alternatively, you can place down a crate that wouldn't have the vest in question already in it, name it 'test' and after you start the preview, put the following line of code into the debug console and execute it:
test addItemCargo ["V_ChestrigB_rgr", 1];
Observe that the vest isn't put into the crate.

I copy and pasted the class name from the config viewer