Null Reference Exception in Visual Studio Debugging

Question

I am trying to test some code and now visual studio is throwing a null reference exception on the following line:

List<int> liveIds = new List<int>();

I am starting to think that visual studio has old code that it is looking at because no matter how I have tried to declare this line it continues to throw a null reference exception on this line.

Anyone know something that I might be missing?

UPDATE: ok so I changed out the variable and now I can't get the same error to happen on the previous line. Now it is happening on this line.

There is no chance for NullReferenceException in the above line, It looks fine — sujith karivelil
– sujith karivelil, Commented Jan 19, 2017 at 3:43
This is the problem. I honestly can not see why it is giving me this error. That is why I feel like VS must be loading a cached assembly possibly. Where I had other code that might have had an error. — spinon
– spinon, Commented Jan 19, 2017 at 3:44
you might do it already but did you try to restart VS? you know sometimes VS just act weird. — Circle Hsiao
– Circle Hsiao, Commented Jan 19, 2017 at 3:47
The exception is being thrown in a dependency, not in your code per se. It is likely a config issue with that dependency. — Brian Driscoll
– Brian Driscoll, Commented Jan 19, 2017 at 4:34

spinon · Accepted Answer · 2017-01-19 05:26:15Z

2

Ok so after some testing, things worked once I refactored the code and extracted the following code to a new method:

        // remove hospitals that are not currently assigned to someone
        hospitalsToCheck.RemoveAll(
            h =>
            {
                return
                    !currentAssignments.Exists(
                        a => a.AssignmentGroup.AssignedUnitIds.Intersect(h.Units.Select(u => u.UnitId)).Any());
            });

It seems that when I had code that was manipulating the list in the same method that it was defined, that is when I was getting the null reference exception.

answered Jan 19, 2017 at 5:26

spinon

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1 Comment

Jack Zhai Over a year ago

glad to know that you find the real reason, if so, would you please mark it as the answer? So it could help other members who meet the same issue as yours. Have a nice day:)

Andrius R. · Accepted Answer · 2018-11-27 10:44:47Z

Maybe the debugger itself is producing the exception.

I got a very similar situation, where i'm assigning a value from a function and the exception occurs right after executing the function (the Locals window indicates that the function does return a value):

var xmlElement = Serialize(data);

From Disassembly it seems that the exception happens immediately after the assignment, but before the next line of code. I'm guessing this is where some debugger code gets executed:

Screenshot of disassembly

Maybe debugger did not expect for that line of code to be executed, because I altered the execution path with "Set Next Statement" command (moved from the "else" block into this one). Same thing happens if I alter the code (remove the "if") while the debug is running, but the problem does not repeat if I rerun the encompassing procedure after the edit.

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