If you are doing Site sync for Stefinity and getting an error “Object reference not set to an instance of an object”. It does not matter what kind of conetent you are trying to sync you will get this error. Just make sure you have set up Sitefinity to sync based on this doc. http://docs.sitefinity.com/81/prerequisites-and-restrictions.
The mane thing you need to do is make sure Feeds & Notifications moudel is acitve on both staging and production. You can activate if from Go to Administration->Modules & Services and install/activate “Feeds & Notifications” module. Once you do that will take care of you sync issue.