Employer exemption from liability when due diligence shown and another committed the offence; accused may be prosecuted instead. Where an employer charged under the Code names another as the actual offender and, after the offence is proved, proves to the court that he exercised due diligence to enforce the Code and that the other person committed the offence without his knowledge, consent or connivance, the other person may be convicted and punished as if he were the employer and the employer shall be discharged from liability; the employer may be examined on oath and his evidence is subject to cross-examination.