Property with init-only setter results in MissingMethodException

[MarcelVersteeg]

Describe the bug In case of read-only properties in the command line options class, where a property is defined as

public string Foo
{
    get;
    init;
}

you will get a MissingMethodException when parsing the command line.

To Reproduce See this fiddle https://dotnetfiddle.net/J05g0c

Expected behavior The exception is not thrown

Additional context The resulting stack trace is as follows:

Unhandled exception. System.MissingMethodException: Cannot dynamically create an instance of type 'Options'. Reason: No parameterless constructor defined.
   at System.RuntimeType.ActivatorCache..ctor(RuntimeType rt)
   at System.RuntimeType.CreateInstanceOfT()
   at System.Activator.CreateInstance[T]()
   at CommandLine.Core.InstanceBuilder.<>c__1`1.<Build>b__1_0(Func`1 f)
   at CSharpx.MaybeExtensions.MapValueOrDefault[T1,T2](Maybe`1 maybe, Func`2 func, T2 noneValue)
   at CommandLine.Core.InstanceBuilder.Build[T](Maybe`1 factory, Func`3 tokenizer, IEnumerable`1 arguments, StringComparer nameComparer, Boolean ignoreValueCase, CultureInfo parsingCulture, Boolean autoHelp, Boolean autoVersion, Boolean allowMultiInstance, IEnumerable`1 nonFatalErrors)
   at CommandLine.Parser.ParseArguments[T](IEnumerable`1 args)
   at Program.Main(String[] args)

[elgonzo]

A small clarification here: It's not the setter being init that's causing the issue.

The issue is triggered by using a setter (regardless of whether it's an init or set setter) while also using a parameterized constructor. Whether this constitutes a bug or an intentional design restriction of option classes i can't tell, because i am not involved with the project, but to me subjectively it seems to be an oversight/bug in the library's logic...