MODEL PENAL CODE
(1) Ignorance or mistake as to a matter of fact or law is a defense if:
(a) the ignorance or mistake negatives the purpose, knowledge, belief, recklessness or negligence required to establish a material element of the offense; or
(b) the law provides that the state of mind established by such ignorance or mistake constitutes a defense.
(2) Although ignorance or mistake would otherwise afford a defense to the offense charged, the defense is not available if the defendant would be guilty of another offense had the situation been as he supposed. In such case, however, the ignorance or mistake of the defendant shall reduce the grade and degree of the offense of which he may be convicted to those of the offense of which he would be guilty had the situation been as he supposed.
(3) A belief that conduct does not legally constitute an offense is a defense to a prosecution for that offense based upon such conduct when:
(a) the statute or other enactment defining the offense is not known to the actor and has not been published or otherwise reasonably made available prior to the conduct alleged; or
(b) he acts in reasonable reliance upon an official statement of the law, afterward determined to be invalid or erroneous, contained in (i) a statute or other enactment; (ii) a judicial decision, opinion or judgment; (iii) an administrative order or grant of permission; or (iv) an official interpretation of the public officer or body charged by law with responsibility for the interpretation, administration or enforcement of the law defining the offense.
(4) The defendant must prove a defense arising under Subsection (3) of this Section by a preponderance of evidence.