When importing borrowers in the staff client, it requires you to specify a borrowers.login_attempts value of '0'. DBD::mysql::st execute failed: Column 'login_attempts' cannot be null [for Statement "INSERT INTO `borrowers` File has branchcode, cardnumber, categorycode, surname, firstname, sort1. Work around: add login_attempts with '0' value. Import works. Might be related to bug 25664?
Tested and working in master.