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NullReferenceException is an error that programmers frequently encounter, and it is often referred to as the Billion Dollar Mistake. This course is designed to assist you in avoiding this error.

You will begin by gaining an understanding of when NullReferenceException is thrown and how to prevent null in your code. You’ll also learn how to employ nullable operators to simplify null checks and use nullable references and the Option wrapper to identify problematic code blocks. Finally, you will explore avoiding NullReferenceException when using specific LINQ methods and designing your C# classes.

Upon completing this course, you’ll have gained the necessary knowledge and skills to effectively address and avoid NullReferenceException issues in your projects.

Mastering NullReferenceException Prevention in C#

So far, we have used language features to avoid `null` and a possible `NullReferenceException`, like `null` checks and nullable operators and references. Let's see how to better design our objects to avoid `null` when representing optional values.

# Avoiding `null` and a possible `NullReferenceException`

Often, we keep all possible combinations of properties of an object in a single class.

For an e-commerce site, we create a `User` class with different properties: `name`, `password`, and `CreditCard`. But we don't need credit card details during a trial period, for example. So we make the credit card optional by allowing it to be `null`. This way, we end up with a class with nullable properties and methods that only should be called when some of those properties aren't `null`.

Let's write a `User` class to represent either regular or premium users. We should only store credit card details for premium users to charge a monthly subscription.

Separate Objects and Separate State

Avoiding null and a possible NullReferenceException

Avoiding `null` and a possible `NullReferenceException`