The null object design pattern

Most object-oriented languages have a way of specifying the nonexistence of some value. In Scala and Java, for example, this could be the null value that can be assigned to an object. Calling any method on an object that is null would result in a NullPointerException, hence developers should be careful and check whether there is such a possibility. These checks, however, could make the source code hard to follow and extend as developers should always be aware. This is where the null object design pattern is helpful. Its purpose is:

Note

To define an actual object that represents the null value and has neutral behavior.

Using null objects removes the need to check whether something is set to null or not. The code becomes much more readable and easy to understand and makes bug occurrence harder.

Class diagram

For the class diagram, let's imagine that we have a system that has to poll a queue for messages. Of course, this queue might not always have anything to offer...