a. It shall not be necessary for the State to negate any exemption or exception set forth in this act in any complaint, information, indictment or other pleading or in any trial, hearing, or other proceeding under this act, and the burden of proof of any such exemption or exception shall be upon the person claiming its benefit.
b. In the absence of proof that a person is the duly authorized holder of an appropriate registration or order form issued under this act, he shall be presumed not to be the holder of such registration or form, and the burden of proof shall be upon him to rebut such presumption.
c. No liability shall be imposed by virtue of this act upon any duly authorized State officer, engaged in the enforcement of this act, who shall be engaged in the enforcement of any law or municipal ordinance relating to controlled dangerous substances.