Apex domains cannot have CNAME records.
Question and response
Question
dig xniel.fr. NS
Answer
xniel.fr. 3 NS nssec.dedibox.fr.
xniel.fr. 3 NS ns0.xniel.fr.
Authority
The response has no authority records.
Additional
ns0.xniel.fr. 3 A 62.210.201.153
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0