# File lib/active_merchant/billing/credit_card_formatting.rb, line 9
      def format(number, option)
        return '' if number.blank?
        
        case option
          when :two_digits  ; sprintf("%.2i", number)[-2..-1]
          when :four_digits ; sprintf("%.4i", number)[-4..-1]
          else number
        end
      end