What type of exception to throw

Question

What typeo of exception would you throw from a readonly property when the object that is being used to return value is null

public class TestClass
{
    SomeObject obj;
    public string NameOfObject 
    {
       get 
       {
            if(obj == null)
            { // what exception type to throw here  }
            return obj.Name;
       }
}

Answer 1

I would throw an InvalidOperationException.

ArgumentNullException i only throw if methods parameters are null.

If the methods parameter is in an invalid state i throw an ArgumentException.

Answer 2

An InvalidOperationException is what I would use in this case, because the access to the property is not valid for the current state of the object.

According to MSDN documentation:
"The exception that is thrown when a method call is invalid for the object's current state."
also:
"InvalidOperationException is used in cases when the failure to invoke a method is caused by reasons other than invalid arguments."

In this case obj is not an argument, which is why I would lean towards "InvalidOperationException"

The reason why I would not throw a NullReferenceException here: If you didnt add any special code, thats the exception that ".Net" would throw, so why add redundant code?

Answer 3

You should not throw NullReferenceException. It is reserved for situations when a null object is dereferenced. In this case, if you were to throw NullReference, you might as well just leave the null check out and let the framework throw it for you when you attempt to access the obj's Name.

I'd throw InvalidOperationException instead.