valid_nz_number?

# File lib/net/imap.rb, line 1666
        def valid_nz_number?(num)
          # [RFC 3501]
          # nz-number       = digit-nz *DIGIT
          #                    ; Non-zero unsigned 32-bit integer
          #                    ; (0 < n < 4,294,967,296)
          num != 0 && valid_number?(num)
        end