In suits brought in behalf of the state, no debt or claim shall be allowed as a setoff other than those which have been exhibited to the Auditor of State and by him or her allowed, except only in cases when it shall be proven to the satisfaction of the court that the defendant at the time is in possession of vouchers which he or she could not produce to the Auditor of State or that he or she was prevented from exhibiting the claims to the Auditor of State in consequence of sickness or absence.