Fuel filler hole question

I just went out to go check the size of the filler hole on the truck, and I feel like something is different. I remember there used to be a brass flap there (like in the picture I've attached). Now, though, it's just a hole. Am I imagining things or being overly paranoid? Or is something genuinely missing from my truck? Mine isn't like the picture below. It's just a hole. Nothing blocking it and I can use a flashlight and look all the way down.