design patterns - How do I create a Null Object in C#

Question

Martin Fowler's Refactoring discusses creating Null Objects to avoid lots of

if (myObject == null)

tests. What is the right way to do this? My attempt violates the "virtual member call in constructor" rule. Here's my attempt at it:

public class Animal
{
    public virtual string Name { get; set; }
    public virtual string Species { get; set; }
    public virtual bool IsNull 
    { 
        get { return false; }
    }
}

public sealed class NullAnimal : Animal
{
    public override string Name
    {
        get{ return "NULL"; }
        set { }
    }
    public override string Species
    {
        get { return "NULL"; }
        set { }
    }
    public virtual bool IsNull
    {
        get { return true; }
    }
}

Answer 1

Go look up the amount of pain that interesting concepts, such as DbNull, have caused and think about if this is actually a good idea.

Protip: if you are constantly checking for null references, you probably should rethink the API a bit to help preclude null objects closer to the top of the stack.

Protip II: having something throw an exception when there is an unexpected null is actually fine and dandy. Things should go boom if you have nulls where there shouldn't be null.