Question

How can I get a NullReferenceException in the following scenario?

 Dim langs As IEnumerable(Of SomeCustomObject) = //some LINQ query
 If langs Is Nothing Then Return Nothing 
 If langs.Count = 1 Then //NullReferenceException here

What am I missing here? Debug shows that langs is really just a LINQ queryresult without any results…

Answer 1

The exception is probably coming from the evaluation of your LINQ query. LINQ queries are evaluated in a lazy fashion: that is, no code is actually executed until you actually use the value.

For example, if you have the following (I don’t know the LINQ syntax for VB, so this is C# but the same thing applies):

string str = null;
IEnumerable<char> chs = from ch in str select ch;
if (chs.Count() == 0) // NullReferenceException here

Also, you will never get a null returned from the creation of the LINQ query so your If langs Is Nothing check is not needed.