NullReferenceException in LINQ Query

Question

I am getting an unusual "NullReferenceException was unhandled by user code" error in this LINQ query:

List<UDIDInfo> d2Android = d2.Where(x.DeviceOS == (byte)DeviceOS.Android).ToList();

I went ahead and added a null check and am still getting the error

List<UDIDInfo> d2Android = d2.Where(x => x.DeviceOS != null && x.DeviceOS == (byte)DeviceOS.Android).ToList();

Note that (byte)DeviceOS.Android and d2 are both not null

Edit (Solution):

List<UDIDInfo> d2Android = d2.Where(x => x != null && x.DeviceOS != null && x.DeviceOS == (byte)DeviceOS.Android).ToList();

Possible duplicate of [What is a NullReferenceException and how do I fix it?](http://stackoverflow.com/questions/4660142/what-is-a-nullreferenceexception-and-how-do-i-fix-it) — Nasreddine, Oct 04 '15 at 09:09

score 7 · Accepted Answer · answered Nov 06 '13 at 20:15

7

What if x is null? That is, the enumerable d2 contains a null item.

Try the following. You shouldn't get any null reference exception.

List<UDIDInfo> d2Android = d2
    .Where(x => x != null)
    .Where(x => x.DeviceOS != null)
    .Where(x => x.DeviceOS == (byte)DeviceOS.Android)
    .ToList();

answered Nov 06 '13 at 20:15

Timothy Shields

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If this is Linq-to-entities, then x can't be null. – user2674389 Nov 06 '13 at 20:16
@user2674389 That's probably true. I didn't even notice the LINQ-to-entities tag since there was no mention in the question. – Timothy Shields Nov 06 '13 at 20:17
Actually Tim's method worked; adding x != null short circuits the query. d2 is a List – Omar Meky Nov 06 '13 at 20:31
@OmarMeky Then the tag ***EntityFramework*** is wrong, since there is nothing related to EntityFramework. – user2674389 Nov 06 '13 at 20:35
Fair enough, I added it since the List came from an EF query but that's irrelevant – Omar Meky Nov 06 '13 at 20:37

score 0 · Answer 2 · answered Mar 09 '21 at 06:58

avoid the argument null exception in LINQ like below

Summaries = (from r in Summaries
          where r.Contains(SearchTerm)
          orderby r
          select r).ToArray();

In this case, if null passed to searchTerm you can check the null expression like below

Summaries = (from r in Summaries
          where string.IsNullOrEmpty(SearchTerm) ||r.Contains(SearchTerm)
          orderby r
          select r).ToArray();

NullReferenceException in LINQ Query

2 Answers2