(a) Proof of lack of record. A written statement, signed by an officer having the custody of an official record or by his deputy, that after diligent search no record or entry of a specified tenor is found to exist in the records of his office, accompanied by a certificate attesting to his custody of the official record relating to such matters, is admissible as evidence that the records of his office contain no such record or entry.

(b) Other proof. This Code section does not prevent the proof of official records or of entry or lack of entry therein by any method authorized by any applicable statutes or by the rules of evidence at common law.