With the Null Object pattern we can eliminate the need to check for null evaluations, and simplify our code.

Oftentimes when we are executing a function on or for a resource, we first check if that resource exist, something like this example from PPP:

Employee e = DB.getEmployee("Bob");
if (e != null && e.isTimeToPay(today))
  e.pay();

According to Martin, this is an ugly an error prone idiom. One method to alleviate errors, is to have the DB.getEmployee function throw an exception instead of returning null; but wrapping such logic in try/catch blocks is usually even uglier than the check for null.

This is where the use of the Null Object pattern can come in handy.

Essentially what we’d do is create an Employee interface that is implemented by both a standard EmployeeImplementation object and also a NullEmployee object. In the EmployeeImplementation we’d have all the variables and methods a standard employee should have for operation; and in the NullEmployee object we’d have all the same variables and methods, yet they’d return or do some form of nothing.

Using this pattern we could then implement the above code as follows:

Employee e = DB.getEmployee("Bob");
if (e.isTimeToPay(today))
  e.pay();

This way we are more communicative about what we are trying to do without the need for control flow in the form of the && operator in our if statement. The implementation of Employee will be of the form of the null object, where of course we do not need to worry about a payment occuring because the pay action is rendered useless inside of the NullEmployee object.