Apex domains cannot have CNAME records.
Question and response
Question
dig amadeus.com. NS
Answer
amadeus.com. 5 NS a6-66.akam.net.
amadeus.com. 5 NS a13-67.akam.net.
amadeus.com. 5 NS a1-46.akam.net.
amadeus.com. 5 NS a18-64.akam.net.
amadeus.com. 5 NS a5-65.akam.net.
amadeus.com. 5 NS a8-67.akam.net.
Authority
The response has no authority records.
Additional
a1-46.akam.net. 2 A 193.108.91.46
a5-65.akam.net. 2 A 95.100.168.65
a6-66.akam.net. 2 A 23.211.133.66
a8-67.akam.net. 2 A 2.16.40.67
a13-67.akam.net. 2 A 2.22.230.67
a18-64.akam.net. 2 A 95.101.36.64
a1-46.akam.net. 2 AAAA 2600:1401:2:0:0:0:0:2e
a5-65.akam.net. 2 AAAA 2600:1480:b000:0:0:0:0:41
a6-66.akam.net. 2 AAAA 2600:1401:1:0:0:0:0:42
a8-67.akam.net. 2 AAAA 2600:1403:a:0:0:0:0:43
a13-67.akam.net. 2 AAAA 2600:1480:800:0:0:0:0:43
a18-64.akam.net. 2 AAAA 2600:1480:4800:0:0:0:0:40
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0