using System;

#nullable enable                

public class Program

{

    public static void Main()

    {

​

        var a = new Test<string>("test");

        var b = a.Prop;

        var c = b.Length;

        var d = default(int);

    }

}

public class Test<T> where T : notnull{

    public T Prop {get;set;}

    public Test(T prop){

        Prop = prop;

    }

}

​