Apex domains cannot have CNAME records.
Question and response
Question
dig amadeus.net. NS
Answer
amadeus.net. 5 NS a6-66.akam.net.
amadeus.net. 5 NS a18-64.akam.net.
amadeus.net. 5 NS a1-46.akam.net.
amadeus.net. 5 NS a5-65.akam.net.
amadeus.net. 5 NS a13-67.akam.net.
amadeus.net. 5 NS a8-67.akam.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0