URI.to_string causes ArgumentError when :port is :undefined

[pjdiiori]

Elixir and Erlang/OTP versions

Erlang/OTP 26 [erts-14.2.3] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:1]

Elixir 1.16.2 (compiled with Erlang/OTP 26)

Operating system

MacOS Sonoma 14.3.1

Current behavior

When parsing/validating a string with URI.new/1, if the string contains "//https://" you receive a URI struct with port: :undefined. Then, if you feed that struct into URI.to_string/1, you get an Argument error.

iex(1)> {:ok, uri} = URI.new("//https://www.example.com")
{:ok,
 %URI{
   scheme: nil,
   userinfo: nil,
   host: "https",
   port: :undefined,
   path: "//www.example.com",
   query: nil,
   fragment: nil
 }}
iex(2)> URI.to_string(uri)
** (ArgumentError) errors were found at the given arguments:

  * 1st argument: not an integer

    :erlang.integer_to_binary(:undefined)
    (elixir 1.15.7) lib/uri.ex:1057: String.Chars.URI.extract_authority/1
    (elixir 1.15.7) lib/uri.ex:1034: String.Chars.URI.to_string/1
    iex:2: (file)
iex(2)>

Expected behavior

I would expect that

1. URI.new/1 should not return :undefined or any other atom for the :port field since its type is defined as nil | :inet.port_number() https://github.com/elixir-lang/elixir/blob/v1.16.2/lib/elixir/lib/uri.ex#L31. I'd think it would return either an error tuple, or a URI struct with port: nil.
2. Or, URI.to_string/1 should handle a URI struct with port: :undefined by returning a string with the URI.