c#: enumeration yielded no result

Asked Jul 31 '18 at 13:48

Active Jul 31 '18 at 13:48

Viewed 34 times

Im setting value in a variable like this:

var billing = context.Payload.QuestionGroupList.Where(x => x.GroupCode.ToLower().Equals("yourinfo"));

But problem is, I get null exception when I query it. Although I have kept a null check but it passes this check and when I expand the resultview I see 'enumeration yielded no result'

I get NULL reference exception since billing is empty on the following line. So my question is what further check I can apply to avoid it?

if (billing != null)
{
   billingAddress = billing.FirstOrDefault().QuestionList.Where(x => x.Code.ToLower().Equals("billingaddressques")).Select(x => new Question { QuestionAnswer = x.QuestionAnswer, Code = x.Code }).ToList();
}

asked Jul 31 '18 at 13:48

Huma Ali

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`billing.FirstOrDefault()` could return `null` aswell. Remember this a linq query on an enumeration never returns `null`. Like where/select/orderby etc.. if there is nothing, it returns an empty enumeration. – Jeroen van Langen Jul 31 '18 at 13:49
@J.vanLangen what check should be added other than `(billing != null)` to avoid null? – Huma Ali Jul 31 '18 at 13:51
You should check to see if `billing` contains any items as well as the null check: `if (billing != null && billing.Any())` – SBFrancies Jul 31 '18 at 13:52
What about `QuestionList`, `x.Code`, etc? – Patrick Hofman Jul 31 '18 at 13:52
@HumaAli `billing.Any()` does the right job. If you use `FirstOrDefault` always check if it return the default. for classes is it `null` – Jeroen van Langen Jul 31 '18 at 13:52
@PatrickHofman assumtions ofcourse, but it looks like a detail table. which probably is created by the db framework – Jeroen van Langen Jul 31 '18 at 13:53
They can be null. @J.vanLangen – Patrick Hofman Jul 31 '18 at 13:53
@PatrickHofman never worked with it, but I wouldn't program it that way... ;-) an empty collection is way different than a `null` – Jeroen van Langen Jul 31 '18 at 13:54

c#: enumeration yielded no result

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