Before we actually look at our code, we will note a few observations about the preceding diagram. It represents a classical case using the null object design pattern. However, nowadays, it is not really used this way in either Java or Scala. For example, Java now supports Optional, which is used instead (assuming people use new versions of the language). In Scala, things are similar—we can and do use Option[Message] instead of null objects. Additionally, we gain all the other nice features of Option such as the ability to use them in pattern matching.
So, as mentioned previously, our code is not really going to use the hierarchy of the preceding class diagram. It just doesn't need it and it will be much simpler. Instead, we ...
