def add_contributor(str, role = "A01")
      contrib = ::ONIX::Contributor.new
      contrib.sequence_number = product.contributors.size + 1
      contrib.contributor_role = role
      contrib.person_name_inverted = str
      product.contributors << contrib
    end
def add_contributor(str, role = "A01")
      contrib = ::ONIX::Contributor.new
      contrib.sequence_number = product.contributors.size + 1
      contrib.contributor_role = role
      contrib.person_name_inverted = str
      product.contributors << contrib
    end
set a new contributor to this product
 str should be the contributors name inverted (Healy, James)