Apex domains cannot have CNAME records.
Question and response
Question
dig optimitel.fr. NS
Answer
optimitel.fr. 2 NS tic.ipnotic-telecom.fr.
optimitel.fr. 2 NS tac.ipnotic-telecom.fr.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0