Null References: The Billion Dollar Mistake - https://www.infoq.com/presentations/Null-References-The-Billion-Dollar-Mistake-Tony-Hoare
Let’s Code Real World App Using Purely Functional Techniques (in Scala) - https://www.youtube.com/watch?v=m40YOZr1nxQ&list=WL&t=0s&index=2