"Object reference not set to an instance of an object" even when I checked null

Question

I have Room and Bed EF classes which each of Room have some Beds.when I use this LINQ statement:

IEnumerable<Room> room=...
if (room == null || !room.Any())
    return null;
return room.SelectMany(r=>r.Beds);

give me this error:

Object reference not set to an instance of an object.

in return line.

Your code looks OK and shouldn't give this error. So try to reproduce it in a small but complete program we can run as well. Most likely you'll find the cause yourself along the way. — Henk Holterman
– Henk Holterman, Commented Jul 13, 2013 at 19:20

YK1 · Accepted Answer · 2013-07-13 19:45:03Z

17

One of your rooms in the enumerable is null. Do this:

return room.Where(r => r != null)
           .SelectMany(r => r.Beds);

answered Jul 13, 2013 at 19:45

YK1

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2 Comments

Offir Over a year ago

for me it was return room.Where(r => r.Beds != null) .SelectMany(r => r.Beds);

Hugo Rocha Over a year ago

Anyone knows why this happens? It works when doing room.Select(x => x.beds) when has a null on it, why selectmany doesnt?

Majid · Accepted Answer · 2013-07-13 19:53:16Z

2

I found out that my Collection of Rooms were not null and also none of Room's Beds were null. problem was that at least one item of my Room Collection was null. so according to YK1's answer I should use:

return room.Where(r => r != null).SelectMany(r => r.Beds);

answered Jul 13, 2013 at 19:53

Majid

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Comments

Community · Accepted Answer · 2017-05-23 11:45:49Z

1

The error can only happen when a Room has Beds == null.

You state: "I only have one Room with two Beds in it" but the question also mentions EF.

So the problem is in the ... in IEnumerable<Room> room=....

When your EF query uses lazy loading the Beds property will be null even if there are records.

For a complete solution you'll have to post all details about the EF part: Code|DB first, the query, which type Context class, EF version etc.

With the latest versions of EF this kind of problem is rare, my guess is that you have a ToList() in the query where you shouldn't.

edited May 23, 2017 at 11:45

CommunityBot

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answered Jul 13, 2013 at 19:31

Henk Holterman

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2 Comments

Majid Over a year ago

but why if(!room.Any(x => x.Beds == null)) give me same error?

Henk Holterman Over a year ago

I don't really know. Unable to tell from what you posted.

Guilherme H. J. · Accepted Answer · 2013-07-13 19:18:09Z

0

You can try to use count too, like this:

IEnumerable<Room> room=...
if (room == null)    // Check for nulls
       return null;
else if (room.count() == 0)     // Check if empty
       return null;
else if(!room.Any(x => x.Beds == null)      // Check if there is no null Beds
       return room.SelectMany(r=>r.Beds);

answered Jul 13, 2013 at 19:18

Guilherme H. J.

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2 Comments

Henk Holterman Over a year ago

A lot of checking but what could be the real cause?

Guilherme H. J. Over a year ago

The count() == 0 would be to replace the !room.Any() i believe.

Venoth01 · Accepted Answer · 2022-07-29 12:01:42Z

0

Please try this..

return room.Where(r => r != null & r.Beds != null).SelectMany(r => r.Beds);

answered Jul 29, 2022 at 12:01

Venoth01

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