§  255.20  Unlawfully  procuring  a  marriage license, bigamy, adultery: defense. In any  prosecution  for  unlawfully  procuring  a  marriage  license,  bigamy,  or  adultery,  it  is an affirmative defense that the defendant  acted under a reasonable belief that both he and the other person to the  marriage or prospective marriage or to the sexual  intercourse,  as  the  case may be, were unmarried.