Half moon shaped object covering iPhone 4s rear camera?

I just bought a second-hand iphone 4s that supposedly wasn't used more than a month, and was in perfect condition. When it arrived I realized the camera had a half moon shaped piece covering the lense. The phone is out of warranty. Any ideas on how to fix this, or if Apple would do it for me since from googling it it seems to be a manufacturer defect? Thanks for the help. 🙂