ensure_nz_number

# File lib/net/imap.rb, line 1457
      def ensure_nz_number(num)
        if num < -1 || num == 0 || num >= 4294967296
          msg = "nz_number must be non-zero unsigned 32-bit integer: " +
                num.inspect
          raise DataFormatError, msg
        end
      end