Where is the oven light lens cover?

I am shopping for an free standing electric stove. As i am shopping and looking at all different brands, I noticed that some ovens have a light bulb inside with no lens cover, but looks as though it is designed to have one. There are holes in the back wall that seem as though you can add this lens part if you want to. Some ovens I see have a lens cover. I took the model numbers and looked up the parts blowout and no lens cover is offered to those ovens which dont have one inside. The ovens that have a lens cover show one in the parts blowout of that model. Isn't this a safety issue? Shouldn't all ovens have a cover over the light bulb inside? I am finding this situation on many different makes and models of electric ovens. Does anyone know what's going on here?