Apex domains cannot have CNAME records.
Question and response
Question
dig merula.net. NS
Answer
merula.net. 5 NS ns1.merula.net.
merula.net. 5 NS ns2.merula.net.
merula.net. 5 NS ns3.merula.net.
merula.net. 5 NS ns4.merula.net.
Authority
The response has no authority records.
Additional
ns1.merula.net. 5 A 217.146.99.250
ns2.merula.net. 5 A 217.146.105.2
ns3.merula.net. 5 A 193.201.42.194
ns4.merula.net. 5 A 174.138.162.179
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0