The person I was responding to (who I recall was disagreeing with me on the more general principle) said something to the effect of "well you're wrong, in common lisp that's indeed how nil is implemented".
I was skeptical and asked for proof of this claim, and they responded clearly angrily with the link to the SBCL repo and said something like "the source code is right there. You can just look it up yourself instead of being so rude. I'm no longer going to interact with you and will delete these comments in 10 minutes."
I think I looked through the source code for a few minutes, but wasn't able to find any evidence of nil being pair of itselves.