It is an exception to the offenses of bribery, solicitation, and buying and selling public office that the benefit involved is a fee prescribed by law to be received by a public servant or any other benefit to which the public servant was lawfully entitled.  Additionally, it is a defense that the benefit was a trivial benefit incidental to personal, professional, or business contacts, which involves no substantial risk of undermining official impartiality, or a lawful contribution made for the political campaign of an elective public servant when the public servant is a candidate for nomination or election to public office.  T.C.A. § 39-16-106.