Hi @soyjuanmalopez, first of all, thanks for your great article at https://medium.com/swlh/clean-architecture-java-spring-fea51e26e00 about clean architecture!
When checking the source code for your example, I think you are not using the validateSelf() method of your abstract SelfValidating.java class. If you want to use it in the Category.java class, you need to directly invoke the extended validation method in your own constructor ((...) this.validateSelf()), for example.
Kind regards!