Suggestion: Don't throw an exception from TzConvert.TryGetTimeZone if the time zone id string is null.

[scotthannen]

I have never contributed to open source. Can I submit this as a PR with the accompanying unit test? I don't know the rules. Do I need a specific branch name?

    public static bool TryGetTimeZoneInfo(string windowsOrIanaTimeZoneId,
        [MaybeNullWhen(false)] out TimeZoneInfo timeZoneInfo)
    {
        if (windowsOrIanaTimeZoneId is null)      // <==== THIS
        {
            timeZoneInfo = null;
            return false;
        }
        // etc
    }