Apex domains cannot have CNAME records.
Question and response
Question
dig nette.pl. NS
Answer
nette.pl. 5 NS ns1.nette.pl.
nette.pl. 5 NS ns2.nette.pl.
Authority
The response has no authority records.
Additional
ns1.nette.pl. 5 A 193.138.118.3
ns2.nette.pl. 5 A 193.138.118.6
ns1.nette.pl. 5 AAAA 2a02:2928:a:0:0:0:0:3
ns2.nette.pl. 5 AAAA 2a02:2928:a:0:0:0:0:6
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0