Sec. 1. (a) A person commits an offense only if he voluntarily engages in conduct in violation of the statute defining the offense. However, a person who omits to perform an act commits an offense only if he has a statutory, common law, or contractual duty to perform the act.
(b) If possession of property constitutes any part of the prohibited conduct, it is a defense that the person who possessed the property was not aware of his possession for a time sufficient for him to have terminated his possession.