If you're getting this error Notice after Installing Divi Supreme than this guide will help you to solve this issue. This is a bug in Divi and we're hoping that it will be solved very soon.
- Deactivate Divi Supreme Plugin, If you've installed both Pro/Free than deactivate both.
- Now Reactivate Divi Supreme Pro/Lite and you'll not face this issue.
Have a great day!