The general issue in an action of debt on a sealed instrument shall be nil debet, and in an action of assumpsit on such instrument it shall be non assumpsit. It shall not be necessary in either case to plead non est factum, but any evidence admissible under a plea of non est factum may be given under the general issue, provided there be filed with such plea of the general issue the affidavit required by section forty-six, article four, chapter fifty-six of this code.