2. Subsection 1 does not require negating a defense:
a. By allegation in the charging document; or
b. By proof, unless the issue is in the case as a result of evidence sufficient to raise a reasonable doubt on the issue.
Unless it is otherwise provided or the context plainly requires otherwise, if a statute outside this title defining an offense, or a related statute, or a rule or regulation thereunder, contains a provision constituting an exception from criminal liability for conduct which would otherwise be included within the prohibition of the offense, that the defendant came within such exception is a defense.