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? — Nasreddine
– Nasreddine, Commented Oct 4, 2015 at 9:09

Timothy Shields · Accepted Answer · 2013-11-06 20:15:31Z

8

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 6, 2013 at 20:15

Timothy Shields

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5 Comments

user2674389 Over a year ago

If this is Linq-to-entities, then x can't be null.

Timothy Shields Over a year ago

@user2674389 That's probably true. I didn't even notice the LINQ-to-entities tag since there was no mention in the question.

Omar Meky Over a year ago

Actually Tim's method worked; adding x != null short circuits the query. d2 is a List<T>

user2674389 Over a year ago

@OmarMeky Then the tag EntityFramework is wrong, since there is nothing related to EntityFramework.

Omar Meky Over a year ago

Fair enough, I added it since the List came from an EF query but that's irrelevant

logeshpalani31 · Accepted Answer · 2021-03-09 06:58:54Z

0

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();

answered Mar 9, 2021 at 6:58

logeshpalani31

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