Null object pattern

In object-oriented computer programming, a null object is an object with no referenced value or with defined neutral (null) behavior. The null object design pattern, which describes the uses of such objects and their behavior (or lack thereof), was first published as "Void Value"

and later in the Pattern Languages of Program Design book series as "Null Object".

Description

Instead of using a null reference to convey the absence of an object (for instance, a non-existent customer), one uses an object which implements the expected interface, but whose method body is empty. A key purpose of using a null object is to avoid conditionals of different kinds, resulting in code that is more focused, and quicker to read and follow – i.e. improved readability.

One advantage of this approach over a working default implementation is that a null object is very predictable and has no side effects: it does nothing.

For example, a function may retrieve a list of files in a folder and perform some action on each. In the case of an empty folder, one response may be to throw an exception or return a null reference rather than a list. Thus, the code expecting a list must verify that it in fact has one before continuing, which can complicate the design.

By returning a null object (i.e., an empty list) instead, there is no need to verify that the return value is in fact a list.