(a) No person shall have in his possession or under his control a knife having a blade two and one-half inches in length or longer. However, this section shall not apply to any person if it appears that he was at the time engaged in a lawful business calling, employment or occupation, or that the circumstances in which he was placed justified a prudent man in possessing such a weapon for the defense of his person, family or property.
(b) Whoever violates this section is guilty of a misdemeanor of the fourth degree.