Apex domains cannot have CNAME records.
Question and response
Question
dig thalesgroup.com. NS
Answer
thalesgroup.com. 5 NS nsc.perf1.com.
thalesgroup.com. 5 NS nsa.perf1.fr.
thalesgroup.com. 5 NS nsb.perf1.com.
thalesgroup.com. 5 NS ns1.thalesgroup.com.
thalesgroup.com. 5 NS ns2.thalesgroup.com.
Authority
The response has no authority records.
Additional
ns1.thalesgroup.com. 5 A 192.54.145.234
ns2.thalesgroup.com. 5 A 192.54.145.235
nsa.perf1.fr. 5 A 81.92.94.100
nsb.perf1.com. 5 A 81.92.95.100
nsc.perf1.com. 5 A 152.89.172.100
ns1.thalesgroup.com. 5 AAAA 2a00:4f40:666:6001:0:ffff:c036:91ea
ns2.thalesgroup.com. 5 AAAA 2a00:4f40:666:6001:0:ffff:c036:91eb
nsa.perf1.fr. 5 AAAA 2a01:c8:100:0:0:0:0:100
nsb.perf1.com. 5 AAAA 2a01:c8:101:0:0:0:0:100
nsc.perf1.com. 5 AAAA 2a09:35c0:102:0:0:0:0:100
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0