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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#

# Preventing a `NullReferenceException`

Now, let's play!

Let's refactor a method that throws a `NullReferenceException`. For this exercise, we'll continue working with a catalog of movies. This time, each movie contains a director and some reviews. Each review has a score and a comment.

When working with collections, we can prevent a `NullReferenceException` by always initializing collections before using them. For example, before trying to add an element to a list, we should initialize it to an empty list.

To complete this exercise, add `null` checks, initialize collections, and use `ArgumentNullException` where appropriate to prevent a `NullReferenceException`.

Follow the instructions in the comments to complete this exercise.

Refactor a function to fix a NullReferenceException.

Exercise: Refactoring a Function to Prevent Null

Preventing a NullReferenceException

Preventing a `NullReferenceException`