#nullable enable
data class B(string? X, string? Y)
{
    static void M1(bool flag)
    {
        B b = new B(""hello"", null);
        if (flag)
        {
            b.X.ToString(); // shouldn't warn
            b.Y.ToString(); // 1
        }

        b = b with { Y = ""world"" };
        b.X.ToString(); // shouldn't warn
        b.Y.ToString();
    }
}