Apex domains cannot have CNAME records.
Question and response
Question
dig wolterskluwer.be. NS
Answer
wolterskluwer.be. 5 NS ns1-38.azure-dns.com.
wolterskluwer.be. 5 NS ns4-38.azure-dns.info.
wolterskluwer.be. 5 NS ns3-38.azure-dns.org.
wolterskluwer.be. 5 NS ns2-38.azure-dns.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0