(a) Except as provided in this chapter, no person shall operate a motor vehicle upon the public highways without an operator's license issued by the Director of Motor Vehicles.
(b) The licensee shall have such license in his immediate possession at all times when operating a motor vehicle and shall display the license upon demand of any peace officer or other person authorized by the Director of Motor Vehicles. It shall be a defense to any charge under this subsection if the person so charged produces in court an operator's license theretofore issued to such person and valid at the time of his arrest.