'Return safe defaults in case the model has been deactivated.'

@staticmethod
def defaults():

    dummy = S3ReusableField('dummy_id', 'integer', readable=False, writable=False)
    dummy_listref = S3ReusableField('dummy_id', 'list:reference', readable=False, writable=False)
    return dict(hrm_course_id=(lambda **attr: dummy('course_id')), hrm_skill_id=(lambda **attr: dummy('skill_id')), hrm_multi_skill_id=(lambda **attr: dummy_listref('skill_id')))
