List Find() throws Null Exception but should give an empty string

Question

In C#, I have a List that has a fixed number of items, 6 to be precise. These are called out in a Razor template, by using a Find(). However, if that Find cannot find the associated list item, it throws a NullReference exception.

The problem is, if an item doesn't exist, then the view won't load.

I need it to instead provide an empty string to the variable.

I've tried:

var video1 = Model.Videos.FirstOrDefault(x => x.VideoType == "Video1") ?? string.Empty;

But this still returns null.

Could anybody help in getting this to work?

Clue: what's the default value of a string? It's not an empty string. Or Model or Videos could be null. — ManoDestra, Jun 30 '16 at 23:17
I don't even know how that compiles.... `Videos` is obviously a complex class, yet somehow you are null coalescing to a string? — TyCobb, Jun 30 '16 at 23:20
@TyCobb, because he used a `var`. One of the egregious reasons not to use `var`. — GreatAndPowerfulOz, Jun 30 '16 at 23:22
@Great.And.Powerful.Oz Negative. It's figured out at compile time, not at runtime. `var` is safe and awesome. =) — TyCobb, Jun 30 '16 at 23:22
@TyCobb. You are correct, but that is the reason it 'compiles'. Don't get me wrong, I use `var` all the time. I also try to make sure it's obvious what `var` should be. — GreatAndPowerfulOz, Jun 30 '16 at 23:25
@JamesMonger No, it should be creating the error below. It's not `var`, changing it `object` should still cause the issue. CS0019 -> https://msdn.microsoft.com/en-us/library/a63h61ky.aspx — TyCobb, Jul 01 '16 at 15:27

score 3 · Accepted Answer · answered Jun 30 '16 at 23:22

You could use the null-propagation operator as described in C# : The New and Improved C# 6.0

An example of usage would be:

var video1 = Model?.Videos?.FirstOrDefault(x => x.VideoType == "Video1") ?? string.Empty;

The above will ensure that no NullReferenceException will be thrown when Model or Videos are null.

score 1 · Answer 2 · answered Jun 30 '16 at 23:21

It's throwing a NullReferenceException because you are trying to get a property/call a function on a null object.

Looking at your code, we are calling Videos on Model, and then calling FirstOrDefault on Videos.

A NullReferenceException being thrown means that either:

Model is null, so when you call Model.Videos you get a NullReferenceException (because you cannot get the property Videos of null)
Videos is null, so when you call Videos.FirstOrDefault you get a NullReferenceException (because you cannot call the function FirstOrDefault on null.

List Find() throws Null Exception but should give an empty string

2 Answers2