If requested by the judge trying the case, attorneys for the Commonwealth and all city and town attorneys whose general duties include the prosecution of offenses which are reportable by the courts to the Department under § 46.2-383, shall appear on behalf of the Commonwealth or the locality in any contested criminal case wherein a resulting conviction is required to be reported to the Department under § 46.2-383. The failure of the attorney to appear shall, in no case, affect the validity of any conviction.