The null object

The null object is a special object that is not an instance of any class, but that can be stored in a slot intended for any class of object. This is very much like the NULL pointer in C. This is useful when you do not yet have an object to store in a particular slot.

In Prolog, the null is represented by the atom null.

Note that because the null object is not really an object of any class, you cannot determine its class with class_of/2. Unless noted otherwise, when we write of an object in this document, we do not include the null object.