Apex domains cannot have CNAME records.
Question and response
Question
dig nepustil.de. NS
Answer
nepustil.de. 5 NS ns.nepustil.com.
nepustil.de. 5 NS ns1.nepustil.net.
nepustil.de. 5 NS ns.nepustil.de.
nepustil.de. 5 NS ns1.ispeg.eu.
Authority
The response has no authority records.
Additional
ns.nepustil.de. 5 A 212.71.200.209
ns.nepustil.de. 5 AAAA 2001:14f8:8:0:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0