NullReferenceException vs ArgumentNullException

Question

I was reading this post where the answerer mentioned he prefered ArgumentNullException over NullReferenceException.

MSDN mention that for NullReferenceException:

The exception that is thrown when there is an attempt to dereference a null object reference.

On ArgumentNullException they say:

The exception that is thrown when a null reference (Nothing in Visual Basic) is passed to a method that does not accept it as a valid argument.

The answerer seems to say that you can use either.

Is there any reason or any case where I should choose one over the other?

P.S.

I know this question could be opinion based. I want fact, context and situation. I am not interested by personnal preference.

Answer 1

If you are explicitly throwing the exception in your code, you should choose ArgumentNullException.

NullReferenceException is thrown automatically by the CLR when a null reference / pointer is dereferenced:

unsafe
{
    int* ptr = null; // Null pointer.
    int val = *ptr; // NullReferenceException thrown.
}

This most commonly happens when method or property is called on a null reference:

string text = null;
string substring = text.Substring(0, 2); // NullReferenceException thrown.

In most cases, NullReferenceException should not be explicitly thrown in code.

ArgumentNullException is used to check for cases when a null reference is passed as a parameter, usually to prevent a NullReferenceException.

static string FirstTwo(string value)
{
    if (value == null)
    {
        throw new ArgumentNullException(nameof(value));
    }
    return value.Substring(0, 2); // without the original check, this line would throw a NullReferenceException if value were null.
}

The purpose of this check is to clearly let the caller know that null was passed and null is not allowed. Otherwise, if you simply let the NullReferenceException be thrown, the caller would only see

Object reference not set to an instance of an object

which is not as meaningful as this (when using the check):

Value cannot be null. Parameter name: value