Open document. Search text "Musí být uvedeno odpovídající číslo". The list displays the texts "NULL".
Created attachment 56100 [details]
Thanks for bugreport
not reproduced in 3.3.4 and 3.5.3 on Fedora 64 bit
Please, verify if in last version of LibreOffice still reproducible
Not reproduced in:
LO 22.214.171.124. - Debian 32 bit
Version 126.96.36.199.alpha0+ (Build ID: 6736ca4) - Debian 32 bit