In 1965, renowned computer scientist Sir Anthony Hoare designed a type system for an object-oriented language where the goal was to ensure that all use of references would be safe. Accomplishing this seemed fine until he, tempted by its ease of implementation, invented the null reference. Years later, he apologized for doing so and called it his billion-dollar mistake. Unfortunately, Hoare seems unwilling to pay us back, and this mistake still costs your project money. This talk will explore why using the null reference leads to confusion and chaos and how to avoid it.