def subtitle=(str)
      composite = product.titles.first
      if composite.nil?
        composite =  ONIX::Title.new
        composite.title_type = 1
        product.titles << composite
      end
      composite.subtitle = str
    end
def subtitle=(str)
      composite = product.titles.first
      if composite.nil?
        composite =  ONIX::Title.new
        composite.title_type = 1
        product.titles << composite
      end
      composite.subtitle = str
    end
set a new subtitle