Has Cloudflare created a blacklist on their DNS server of entries they won't resolve?

EDIT I just looked this up. Seems like, in this specific instance, Cloudflare is contractually bound by the following:

"The party operating the resolver should not by default block or filter domains unless specifically required by law in the jurisdiction in which the resolver operates. Mozilla will generally seek to work with DNS resolvers that provide unfiltered DNS responses and, at its discretion, may remove from consideration resolvers subject to legal filtering obligations, depending on the scope and nature of those obligations."