Apex domains cannot have CNAME records.
Question and response
Question
dig baupart.de. NS
Answer
baupart.de. 5 NS ns1069.ui-dns.com.
baupart.de. 5 NS ns1047.ui-dns.biz.
baupart.de. 5 NS ns1061.ui-dns.de.
baupart.de. 5 NS ns1082.ui-dns.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0