The Robert C. Martin Clean Code Collection (Collection)

This is called the SPECIAL CASE PATTERN [Fowler]. You create a class or configure an object so that it handles a special case for you. When you do, the client code doesn’t have to deal with exceptional behavior. That behavior is encapsulated in the special case object.

When we return null, we are essentially creating work for ourselves and foisting problems upon our callers.

you are tempted to return null from a method, consider throwing an exception or returning a SPECIAL CASE object instead.