Apex domains cannot have CNAME records.
Question and response
Question
dig assurance-maladie.fr. NS
Answer
assurance-maladie.fr. 5 NS dns1.cscdns.net.
assurance-maladie.fr. 5 NS dns2.cscdns.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0