#588 – A Default Parameter Value Can Be Null

When defining optional parameters and providing a default value for the parameter, you can use a value of null for a reference-typed parameter.  null is actually the only valid default value that you can use for a reference-typed parameter.

        static void LogDogInfo(Dog myDog, Dog anotherDog = null)
        {
            Console.WriteLine("My dog is {0}", myDog.Name);
            if (anotherDog != null)
                Console.WriteLine("  And there is also {0}", anotherDog.Name);
        }

        static void Main()
        {
            Dog dog1 = new Dog("Kirby", 15);
            Dog dog2 = new Dog("Jack", 17);

            LogDogInfo(dog1);
            LogDogInfo(dog2, dog1);
        }