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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#

## `NullReferenceException` and `FirstOrDefault()`

Now, let's practice preventing a `NullReferenceException` when working with LINQ `XOrDefault` methods.

For this exercise, the `Movie` class contains a genre and some reviews. And the new `Review` class has a score and a comment. This time, we have a list of action movies and comedies with good and bad ratings.

To complete this exercise, think of more than one way of fixing a `NullReferenceException`. Feel free to use plain `null` checks, nullable operators, `XOrDefault()` with safe defaults, or `XOrNone()`.

# `NullReferenceException` and `FirstOrDefault()`

Now, let's practice preventing a `NullReferenceException` when working with LINQ `XOrDefault` methods.

For this exercise, the `Movie` class contains a genre and some reviews. And the new `Review` class has a score and a comment. This time, we have a list of action movies and comedies with good and bad ratings.

To complete this exercise, think of more than one way of fixing a `NullReferenceException`. Feel free to use plain `null` checks, nullable operators, `XOrDefault()` with safe defaults, or `XOrNone()`.

Exercise: LINQ XOrDefault Methods

NullReferenceException and FirstOrDefault()

`NullReferenceException` and `FirstOrDefault()`