Apex domains cannot have CNAME records.
Question and response
Question
dig 128-191.151.62.149.in-addr.arpa. NS
Answer
128-191.151.62.149.in-addr.arpa. 5 NS nsb.mydreams.cz.
128-191.151.62.149.in-addr.arpa. 5 NS nsa.mydreams.cz.
128-191.151.62.149.in-addr.arpa. 5 NS nsc.mydreams.cz.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0