def zlib_compression_level(value)
      if /\A-?\d+\z/ =~ value
        i = value.to_i

        if i >= -1 && i <= 9
          return i
        end
      end

      log_warn("#{value} is not a valid zlibCompressionLevel")
      nil
    end
def zlib_compression_level(value)
      if /\A-?\d+\z/ =~ value
        i = value.to_i

        if i >= -1 && i <= 9
          return i
        end
      end

      log_warn("#{value} is not a valid zlibCompressionLevel")
      nil
    end
Parses the zlib compression level.

 @param value [ String ] The zlib compression level string.

 @return [ Integer | nil ] The compression level value if it is between -1 and 9 (inclusive),
   otherwise nil (and a warning will be logged).