def to_xml(options = {})
      subscriptions.each {|s| s.currency = nil}
      adjustments.each   {|a| a.currency = nil}
      super(options)
    end
def to_xml(options = {})
      subscriptions.each {|s| s.currency = nil}
      adjustments.each   {|a| a.currency = nil}
      super(options)
    end
TODO
 This is a temporary solution which allows us to
 embed these resources in a purchase without changing their
 interface. It will be removed once we get rid of default_currency.