The null object pattern
The null object pattern is one of the lightest patterns covered in this book. Sometimes, it is considered just a particular case of the strategy pattern, but it has its own section, given the importance it has in practice.
If we develop programs using a test-driven approach, or if we simply want to develop a module without having the rest of the application, we can simply replace the classes we don't have with a mock class, which has the same structure but does nothing.
Implementation
In the following diagram, we can see that we simply create a NullClass, which can replace the real class in our program. As mentioned before, this is just a particular case of the strategy pattern in which we choose the strategy of doing nothing. The class diagram is as follows:
