The school_classes attribute and others must be allowed to be set to an empty value.
With this change the test "test_12_modify_teacher_remove_all_classes" in ucs-test-ucsschool/94_ucsschool-api-kelvin/03_user_resource succeeds: [feature/kelvin aecc77820] Bug #50710: allow setting attribute to empty value
Tests green: OK Function works: OK
A Kelvin API app with the changes in this bug has been published.