Can't find why do I have a null reference exception

Question

Below is the code and the problematic line.

When I hover with the mouse on src.EnergyServiceLevel, it shows that it's null. How can that be if I'm checking for null in the previous line?

My guess was that maybe there are threads that making the problem so I've add a lock, but it didn't helped.

public static ServiceLevelsGroup SafeClone(this ServiceLevelsGroup src) {
  ServiceLevelsGroup res = null;
  lock (_locker) {
    if (src != null) {
      res = new ServiceLevelsGroup();
      if (src.EnergyServiceLevel != null) {
        res.EnergyServiceLevel = new ServiceLevelInfo { ServiceGrade = src.EnergyServiceLevel.ServiceGrade };

        if (src.EnergyServiceLevel.Reason != null)
          res.EnergyServiceLevel.Reason = src.EnergyServiceLevel.Reason;
      }
    }
  }

  return res;
}

The exception occurs at the res.EnergyServiceLevel = ... line in the above code.

Here's a screenshot of the exception occurring in debug mode:

Screenshot of exception while debugging

Could you copy the code into your post instead of posting an image? The text is too small to read. — hammar
– hammar, Commented May 8, 2011 at 15:15
possible duplicate of What is a NullReferenceException in .NET? — John Saunders
– John Saunders, Commented May 8, 2011 at 15:24
I'm guessing that, since this is an extension method, that ServiceLevelsGroup/ServiceLevelInfo aren't classes in your control? In which case, the exception might be coming from within the ServiceLevelInfo constructor - what happens if you open the "View Detail..." link, and drill into appropriate InnerExceptions? — Damien_The_Unbeliever
– Damien_The_Unbeliever, Commented May 8, 2011 at 15:30
@hammar: you can watch the image directly to have a full-scale view. — Arseni Mourzenko
– Arseni Mourzenko, Commented May 8, 2011 at 15:32

Stuart · Accepted Answer · 2011-05-08 15:26:09Z

2

Your code shows lock(_locker) - so it looks like you're in a multithreaded environment. Can you check that nothing else is NULLing your variable? i.e. that everything else is also calling lock(_locker) correctly?

answered May 8, 2011 at 15:26

Stuart

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3 Comments

brianpeiris Over a year ago

+1 A lock is only useful if you lock the setter as well. Although, since the OP is defining an extension method, he/she probably doesn't have access to the original code.

Erez Over a year ago

I think you're the closest to the real thing, once i get to worl again i'll check maybe I didn't lock properly in other parts of the code.

Stuart Over a year ago

thanks - if it's not a locking issue, then do use "view detail" and take a look at the call stack for the exception - it might just be somewhere inside the evaluation of the property.

Erick Petrucelli · Accepted Answer · 2011-05-08 15:22:56Z

1

Maybe your NULL is at res.EnergyServiceLevel.

answered May 8, 2011 at 15:22

Erick Petrucelli

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1 Comment

BrokenGlass Over a year ago

This wouldn't cause a NullReferenceException

Dulini Atapattu · Accepted Answer · 2011-05-08 15:42:01Z

0

src.EnergyServiceLevel.ServiceGrade may be null

Moving mouse pointer to each reference will exactly show you which is null.

answered May 8, 2011 at 15:42

Dulini Atapattu

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2 Comments

BrokenGlass Over a year ago

This wouldn't cause a NullReferenceException

BrokenGlass Over a year ago

assigning a null value is perfectly legal

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