Apex domains cannot have CNAME records.
Question and response
Question
dig croisieres.fr. NS
Answer
croisieres.fr. 5 NS ns-991.awsdns-59.net.
croisieres.fr. 5 NS ns-1605.awsdns-08.co.uk.
croisieres.fr. 5 NS ns-160.awsdns-20.com.
croisieres.fr. 5 NS ns-1517.awsdns-61.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0