[Koha] Can't call method "biblioitemnumber" on an undefined value

Hi We are using Debian GNU/Linux 12 with Koha 24.05.05. When running script "search_for_data_inconsistencies.pl" it shows only the following message: Can't call method "biblioitemnumber" on an undefined value at /usr/share/koha/bin/maintenance/search_for_data_inconsistencies.pl line 152. What does it mean, how can we find out what's the problem here? Best wishes: Michael -- Geschäftsführer · Diplombibliothekar BBS, Informatiker eidg. Fachausweis Admin Kuhn GmbH · Pappelstrasse 20 · 4123 Allschwil · Schweiz T 0041 (0)61 261 55 61 · E mik@adminkuhn.ch · W www.adminkuhn.ch