def compression_level(val = NULL)
      if null?(val)
        @compression_level || 9
      else
        unless val.is_a?(Integer) && 1 <= val && 9 >= val
          raise InvalidValue.new(:compression_level, "be an Integer between 1 and 9")
        end

        @compression_level = val
      end
    end
def compression_level(val = NULL)
      if null?(val)
        @compression_level || 9
      else
        unless val.is_a?(Integer) && 1 <= val && 9 >= val
          raise InvalidValue.new(:compression_level, "be an Integer between 1 and 9")
        end

        @compression_level = val
      end
    end
Compression level (1-9) to use (-Z).

 @example
   compression_level 1

 @param [Integer] val
   level of compression (1, .., 9)

 @return [Integer]
   level of compression for this package