Apex domains cannot have CNAME records.
Question and response
Question
dig code-planet.de. NS
Answer
code-planet.de. 2 NS ns1.smart-weblications.de.
code-planet.de. 2 NS ns3.smart-weblications.de.
code-planet.de. 2 NS ns2.smart-weblications.de.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0