Evidence of former threats upon plea of self-defense

In any case of assault, assault and battery, or affray in which the plea of the defendant is self-defense, evidence of former threats against the defendant by the person alleged to have been assaulted by him, if such threats shall have been communicated to the defendant before the altercation, shall be competent as bearing upon the reasonableness of the claim of apprehension by the defendant of bodily harm, and also as bearing upon the amount of force which reasonably appeared necessary to the defendant, under the circumstances, to repel his assailant.