using System;

​

public static class CarExtensions

{

    public static void Honk(this Program.Car car)

    {

        Console.WriteLine("Car with make: " + car.make + " honks. Honk! Honk!");

    }

}

​

public class Program

{

    public class Car

    {

        public int make { get; set; }

​

        public Car(int make)

        {

            this.make = make;

        }

    }

​

    public static void Main()

    {

        Car car = new Car(1999);

        Car carNull = null;

        // Here we are going to honk 1 and try to honk a 2nd time

        car.Honk();

        carNull?.Honk();

        // The second car is null, so only 1 honk.

        Console.WriteLine("I only heard one honk :(");

        // Here we are going to get a null reference

        carNull.Honk();

        // Conclusion: the extended object is always defined

    }

}