using System;

class Foo {
    void M(object[] xs) {
        IFormattable s1 = $"{null}"; // Create("{0}", new object[1])
        IFormattable s2 = $"{xs}";   // Create("{0}", new object[] { xs })

        dynamic nil = null, ys = xs;
        IFormattable d1 = $"{nil}";  // Create("{0}", (object[]) null)
        IFormattable d2 = $"{ys}";   // Create("{0}", (object[]) xs)
    }
}

namespace System.Runtime.CompilerServices {
    public static class FormattableStringFactory {
        public static IFormattable Create(string format, params object[] xs) => null;
    }
}