using System;

​

new Derived().Go();

​

class Base

{

    public virtual void Write(int i) => Console.WriteLine($"int i = {i}");

}

​

class Derived : Base

{

    public override void Write(int i) => base.Write(i);

    public void Write(int? i) => Console.WriteLine($"int? i = {i}");

    public void Go() => Write((int?) null);

}