Imagine any .NET codebase you have worked on. What would be the most common usage of if statement in this code? Given the notion of The Billion Dollar Mistake, I bet it is the null check. Reference types in .NET are allocated on the managed heap, so when an instance of such a type is assigned to a variable, this variable essentially points to an adress in this managed heap. The default value of such a variable is null, meaning that it points to nothing and can’t be dereferenced. For instance, if you write a method with a reference type argument, you can’t always predict how this method is going to be invoked and there is no guarantee that it won’t be a null value. To protect your code from an unexpected NullReferenceException, you would typically write something like this: