Null Object
Where an object requires a collaborator object which does nothing.
Where there is a need to ignore the difference between a collaborator that does nothing and a real collaborator.
Applications where null is to be handled as an object that does nothing. (AWT’s layout policy?)
Smalltalk’s MVC (Model-View-Controller).
Code doesn’t have to specifically handle a null reference.
Null behaviour is reusable and the null object can be shared.