The warning [WARN] Use of uninitialized value in concatenation (.) or string at /kohadevbox/koha/opac/opac-search.pl line 600. appears in plack-opac-error.log To reproduce in KTD: 1. Observe plack-opac-error.log. 2. Go to Advanced search in OPAC. 3. Select any of item type ("Limit to any of the following:") in tab "Item type" and perform search (do not enter any "Search for:" terms). 4. Warning appears in plack-opac-error.log.