Rule 4521. Lack of record. A statement signed by an officer or a deputy of an officer having legal custody of specified official records of the United States or of any state, territory or jurisdiction of the United States, or of any court thereof, or kept in any public office thereof, that he has made diligent search of the records and has found no record or entry of a specified nature, is prima facie evidence that the records contain no such record or entry, provided that the statement is accompanied by a certificate that legal custody of the specified official records belongs to such person, which certificate shall be made by a person described in rule 4540.