_Strategies to Get Rid of NullReferenceException.png

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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#

When calling a method on an uninitialized object reference

When accessing a property or field of an uninitialized object reference

When passing `null` as a parameter to a method that uses that parameter

**(Select all that apply.)** When is a `NullReferenceException` thrown?

(Select all that apply.) When is a <code>NullReferenceException</code> thrown?

**(True or False)** The code below throws a `NullReferenceException`:

```csharp
var titanic = new Movie("Titanic", 1997, null);
Console.WriteLine(titanic.Director.Name);

record Movie(string Name, int ReleaseYear, Director Director);
record Director(string Name, DateTime BirthDate);
```

(True or False) The code below throws a <code>NullReferenceException</code>:
<pre><code class="language-csharp">var titanic = new Movie(&quot;Titanic&quot;, 1997, null);
Console.WriteLine(titanic.Director.Name);

record Movie(string Name, int ReleaseYear, Director Director);
record Director(string Name, DateTime BirthDate);
</code></pre>

**(True or False)** The code below throws a `NullReferenceException`:

```csharp
var titanic = new Movie("Titanic", 1997, 7.9f);
Console.WriteLine(titanic.AwardsWonCount);

record Movie(string Name, int ReleaseYear, float Rating)
{
    public int AwardsWonCount { get; set; }
    public string[] Genres { get; set; }
}
```

(True or False) The code below throws a <code>NullReferenceException</code>:
<pre><code class="language-csharp">var titanic = new Movie(&quot;Titanic&quot;, 1997, 7.9f);
Console.WriteLine(titanic.AwardsWonCount);

record Movie(string Name, int ReleaseYear, float Rating)
{
 public int AwardsWonCount { get; set; }
 public string[] Genres { get; set; }
}
</code></pre>

**(True or False)** The code below throws a `NullReferenceException`:

```csharp
var titanic = new Movie("Titanic", 1997, 7.9f);
Console.WriteLine(titanic.Genres[0]);

record Movie(string Name, int ReleaseYear, float Rating)
{
    public int AwardsWonCount { get; set; }
    public string[] Genres { get; set; }
}
```

(True or False) The code below throws a <code>NullReferenceException</code>:
<pre><code class="language-csharp">var titanic = new Movie(&quot;Titanic&quot;, 1997, 7.9f);
Console.WriteLine(titanic.Genres[0]);

record Movie(string Name, int ReleaseYear, float Rating)
{
 public int AwardsWonCount { get; set; }
 public string[] Genres { get; set; }
}
</code></pre>

**(True or False)** This is the correct way of fixing a `NullReferenceException`:

```csharp
try
{
    var movie = FindMovieOrNull();
    Console.WriteLine(movie.Name);
}
catch (NullReferenceException)
{
    Console.WriteLine("Something bad happened");
}
```

(True or False) This is the correct way of fixing a <code>NullReferenceException</code>:
<pre><code class="language-csharp">try
{
 var movie = FindMovieOrNull();
 Console.WriteLine(movie.Name);
}
catch (NullReferenceException)
{
 Console.WriteLine(&quot;Something bad happened&quot;);
}
</code></pre>

Evaluate yourself on what you have learned about the NullReferenceException.

Strategies to Get Rid of NullReferenceException

Quiz on NullReferenceException