Delete the "All (null)" group from Contacts

This was a question I had, but now I think has become an answer for anyone with this question.

I was getting ready to ask what this Group was and why it could not be deleted, until I finally figured out what it was and potentially what else might cause it.

I currently have an iCloud email account as well as a corporate email account (through Microsoft Exchange / Office 365). I thought the problem had something to do with my work account, but that was not the problem. I also have my Facebook account activated (to show Facebook events in my Calendar, and LinkedIn activated as well. You can see if any of these Social Media accounts are active in System Preferences > Internet Accounts. Turned out that the All (null) group is actually my LinkedIn contact list - so they are mostly all duplicates of my iCloud contacts (plus lots more), and the info in those contacts doesn't necessarily match - it was annoying.

Solution was simple - just deactivate the LinkedIn account. There is no reason for me to have it active in my Contact app, you may be different. I didn't have Facebook contacts activated, but this may cause a similar issue.

Hope that helps someone!