In all actions brought on behalf of the state, no debt shall be allowed against the state as a set-off unless it has been exhibited to the director of the department of administration and by him allowed or disallowed. A debt may be allowed as a set-off when it is proved to the satisfaction of the court that the defendant, at the time of trial, is in possession of vouchers which he could not produce to the department of administration, or that he was prevented from exhibiting the claim to the department of administration by absence from the state, sickness or unavoidable accident.
A.R.S. § 35-188