Can you capture the name of the object that throws a NullReferenceException?

Question

Is there a way to find out what specific object caused a NullReferenceException? I've read the page about troubleshooting NullReferenceExceptions and it talks about inspecting variables in the debugger and looking at the exception message.

What if the exception was thrown in production code so you can't run a debugger to inspect the variables? The exception message shows the stack trace so you can see what method the exception was thrown in, but it does not say which specific object was null.

I'd like to be able to add the name of the object that was null to the error message so that when I'm looking into reports from users and I come across a NullReferenceException, I can easily see what object was null and fix it. Does anyone know of a way to do this?

I also found this question which asked the same thing, but it was from 2011 and I don't know if anything has changed since then.

Edit: The question that this is flagged as a duplicate is indeed a duplicate but is also very old (2008). Has anything changed since then?

Edit 2: I found this when googling this question. Visual Studio can tell you what threw the NullReferenceException; is there any way to tap into this to add it to a log file?

Answer 1

It should be relatively easy to figure out given the stacktrace, but a better approach would be to include "validation" or parameters and/or null checks in your code and explicitly throw a ArgumentNullException yourself before you try to access a member of a variable that may not has been initialized. You can then supply the name of the uninitialized object:

if (obj == null)
    throw new ArgumentNullException(nameof(obj));

It's a common practise to perform these checks on arguments in both constructors and methods, e.g:

public void SomeMethod(SomeType someArgument)
{
    if (someArgument == null)
        throw new ArgumentNullException(nameof(someArgument));

    //you will never get there if someArgument is null...
    var someThing = someArgument.SomeMember;

    if (someThing == null)
       throw new ArgumentException("SomeMember cannot be null.", nameof(someArgument));
    ...
}