In all suits brought in behalf of the state, no debt or request for payment or reimbursement shall be allowed against the state as a setoff unless it has been exhibited to the Director of Administrative Services and allowed or disallowed by him or her except only in cases when it is proved to the satisfaction of the court that the defendant at the time of the trial is in possession of vouchers which he or she could not produce to the director or that he or she was prevented from exhibiting the requests to the director by absence from the state, sickness, or unavoidable accident. The director shall in no case audit a request or setoff which is not provided by law.