def convert number
      raise_on_type_mismatch number
      check = self.of(number)
      if number.is_a?(String) or check.is_a?(String)
        number.to_s << self.of(number).to_s
      else
        convert_to_int(number) * 10 + self.of(number)
      end
    end
def convert number
      raise_on_type_mismatch number
      check = self.of(number)
      if number.is_a?(String) or check.is_a?(String)
        number.to_s << self.of(number).to_s
      else
        convert_to_int(number) * 10 + self.of(number)
      end
    end
Transforms a number by appending the ISBN-10 checksum digit

 @example
   Sjekksum::ISBN10.convert("147743025") #=> "1477430253"
   Sjekksum::ISBN10.convert("193435600") #=> "193435600X"

 @param  number [Integer, String] number without a checksum

 @return [Integer, String] final number including the checksum