There was an introduced X-Base-Total-Count header for REST API in Bug 27353. When used from external plugins and "base_total" not provided (is it mandatory?) all logs are heavily filled with: [WARN] Use of uninitialized value $_ in transliteration (tr///) at /usr/share/perl5/Mojo/Headers.pm line 43. It's because X-Base-Total-Count comes with "undef" as I debugged, what solution to choose: A. should we demand this value from plugin creators? B. or should we add this (not "0" as default, anyway, right?): my $base_total = $args->{base_total} // $total; to Koha/REST/Plugin/Pagination.pm line 63?