I get the following warning message in plack-error.log:
> Use of uninitialized value $low in numeric lt (<) at /usr/share/koha/lib/Koha/Patron.pm line 1109.
This seems to happen because in /cgi-bin/koha/admin/categories.pl you can set "Age required" field to be empty and then in the is_valid_age subroutine in Patron.pm we compare patroncategory->dateofbirthrequired to numeric value and empty string or undef is not numeric.
We should either add input validation to categories.pl or convert dateofbirthrequired to numeric value.
*** This bug has been marked as a duplicate of bug 26417 ***