Apex domains cannot have CNAME records.
Question and response
Question
dig hagaziekenhuis.nl. NS
Answer
hagaziekenhuis.nl. 5 NS ns02.nexthost.nl.
hagaziekenhuis.nl. 5 NS ns01.nexthost.nl.
Authority
The response has no authority records.
Additional
ns01.nexthost.nl. 5 A 185.138.80.142
ns01.nexthost.nl. 5 AAAA 2a00:1ac1:812:0:185:138:80:1420
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0