Diagnosis
That haze is almost certainly condensation forming on the inside of the camera's outer lens dome. It happens when there's a temperature difference (like a cold night after a warm day) and a tiny amount of moisture has gotten inside the seal.
How to Fix It
For a mild case, it can sometimes clear on its own as temperatures equalize. You can try gently loosening (but not fully removing) the security screw on the bottom, which might equalize pressure and allow the moisture to escape over a few hours. Then re-tighten it. For a persistent case, you need to dry it out. Power it down, remove it from its mount, and bring it inside to a dry, warm room for 24-48 hours.
If That Didn't Work
If the fogging is permanent or there are visible water droplets inside, the weatherproofing seal around the lens housing has likely failed. This isn't really fixable at home and is a warranty issue.
Heads Up
When re-installing, make sure the main camera body is seated correctly and snugly into the mount/base before tightening the security screw. A poor seat can compromise the weather seal.