validate!

# File activesupport/lib/active_support/duration/iso8601_parser.rb, line 101
        def validate!
          raise_parsing_error("is empty duration") if parts.empty?

          # Mixing any of Y, M, D with W is invalid.
          if parts.key?(:weeks) && parts.keys.intersect?(DATE_COMPONENTS)
            raise_parsing_error("mixing weeks with other date parts not allowed")
          end

          # Specifying an empty T part is invalid.
          if mode == :time && !parts.keys.intersect?(TIME_COMPONENTS)
            raise_parsing_error("time part marker is present but time part is empty")
          end

          fractions = parts.values.reject(&:zero?).select { |a| (a % 1) != 0 }
          unless fractions.empty? || (fractions.size == 1 && fractions.last == @parts.values.reject(&:zero?).last)
            raise_parsing_error "(only last part can be fractional)"
          end

          true
        end