Why do I get a NullException when using any() on byte[] element

Question

I want to test if my byte[] element ImageData contains any data. If there is no data my database shows it as NULL. I tried using the .Any() method, but for some reason this does not work. Why?

I have tried it with the following code

public FileStreamResult ViewImage(int id)
{
    Candidate candidate = _context.Candidate.FirstOrDefault(m => m.Id == id);
    bool hasImage = candidate.ImageData.Any();  // I get the NullException here          

    if (hasImage)
    {
        MemoryStream ms = new MemoryStream(candidate.ImageData);
        return new FileStreamResult(ms, candidate.ImageType);
    }
    return null;            
}

If I use the logic if(candidate.ImageData == null), I get a true or false. I considered using Any() more elegant. Any suggestions?

Does this answer your question? [What is a NullReferenceException, and how do I fix it?](https://stackoverflow.com/questions/4660142/what-is-a-nullreferenceexception-and-how-do-i-fix-it) — derpirscher, Mar 23 '21 at 11:06

Jon Skeet · Answer 1 · 2021-03-23T11:07:12.603

2

It doesn't work because you're calling a method on a null reference... In this case it's an extension method so you'll get an ArgumentNullException instead of a NullReferenceException, but it's behaving exactly as documented.

You can write your own extension method for this if you want:

public class NullSafeEnumerable
{
    public static bool NonNullAny<T>(this IEnumerable<T> source) =>
        source is object && source.Any();
}

(That's not a great name, but you can come up with your own one.)

Or you could use the null-conditional operator:

bool hasImage = candidate.ImageData?.Any() ?? false;

or (equivalently):

bool hasImage = candidate.ImageData?.Any() == true;

edited Mar 23 '21 at 11:07

answered Mar 23 '21 at 10:56

Jon Skeet

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Thanks for the clarification. It is a bit baffling. The object should exist, but the contents may be null? In my case the object did not exist. That is the logic what I've learned. – Charles de M. Mar 23 '21 at 11:00
@CharlesdeM.: It's not clear which object you're talking about - it sounds like the object referred to by the `candidate` variable, but that its `ImageData` returned a null reference rather than a reference to a byte array. That seems entirely reasonable if the value is NULL in the database. Note that a byte array object can't have "null contents", although it can be an array of length 0. – Jon Skeet Mar 23 '21 at 11:04

Sathish Guru V · Accepted Answer · 2021-03-23T12:36:03.283

2

You have to check for the NULL before calling the .Any(), so it won't throw the NullPointerException.

In trival methods you can use

bool hasImage = candidate.ImageData != null && candidate.ImageData.Any();

In the new way you can use the Null Conditional operator C# like

bool hasImage = candidate?.ImageData?.Any() == true;

,which keeps elegant as you wish.

Other way, you can use the Jon's method of null-coalescing operator.

EDIT: As suggested by Jon Skeet, changing the wrong operator name and correcting the last option to de-reference the bool? value.

edited Mar 23 '21 at 12:36

answered Mar 23 '21 at 11:01

Sathish Guru V

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That last approach won't compile, because the expression `candidate?.ImageData?.Any()` has a type of `bool?`, not `bool` - hence the `?? false` in my answer. – Jon Skeet Mar 23 '21 at 11:04
Thanks Sathish for the insight in the `coalescing operator c#`. Very helpful. – Charles de M. Mar 23 '21 at 11:05
That's not the null-coalescing operator though - it's the null-conditional operator. (It's definitely worth knowing about both :) – Jon Skeet Mar 23 '21 at 11:07

score 0 · Answer 3 · answered Mar 23 '21 at 11:04

0

You can also use C# 6.0 feature called Null-conditional operator

bool hasImage = candidate?.ImageData?.Any() == true;

If any of the objects before .Any() is null then the entire expression will return null.

answered Mar 23 '21 at 11:04

Grzegorz Pasnik

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Why do I get a NullException when using any() on byte[] element

3 Answers3