Apex domains cannot have CNAME records.
Question and response
Question
dig spamcluster.nl. NS
Answer
spamcluster.nl. 5 NS ns3.registrar-proxy.nl.
spamcluster.nl. 5 NS ns1.registrar-proxy.nl.
spamcluster.nl. 5 NS ns2.registrar-proxy.nl.
Authority
The response has no authority records.
Additional
ns1.registrar-proxy.nl. 5 A 87.239.8.2
ns2.registrar-proxy.nl. 5 A 87.239.9.3
ns3.registrar-proxy.nl. 5 A 95.179.188.235
ns1.registrar-proxy.nl. 5 AAAA 2001:678:be4:8:0:0:0:2
ns2.registrar-proxy.nl. 5 AAAA 2001:678:be4:9:0:0:0:3
ns3.registrar-proxy.nl. 5 AAAA 2a05:f480:1400:38a2:0:0:0:3
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0