If null.Equals(null) why do I get a NullReferenceException

Question

I have the following line of code -->

var selectedDomainID = lkuDomainType.EditValue.Equals(null) ? string.Empty : lkuDomainType.EditValue;

that is, sometimes, generating a NullReferenceException What I don't understand is why. Isn't the whole point of my code to check for null and if so assign string.empty?? When I check in DEBUG it is stating that EditValue == null so what am I missing?

Thanks

Answer 1

Use lkuDomainType.EditValue == null, otherwise you are trying to call an instance method on a null object. But the better option might be lkuDomainType.EditValue ?? String.Empty. Also watch out for lkuDomainType being null, unless it is a class not an object.

Answer 2

When you use Object.Property and Object is undefined, you are dereferencing a null pointer and that's why you get the exception. Instead, use:

var selectedDomainID = lkuDomainType.EditValue == null ? string.Empty : lkuDomainType.EditValue;

Answer 3

you are trying to call the Equals method on a null object - do it like this instead:

lkuDomainType.EditValue == null

Answer 4

EditValue == null. That means that there is no object there. You cannot call functions on null objects, even if the function is .Equals().

You're better off just saying "(lkuDomainType.EditValue == null)" in this case.

Answer 5

If EditValue is null then you can't call Equals. In this cas you would have to do:

var selectedDomainID = lkuDomainType.EditValue == null ? string.Empty : lkuDomainType.EditValue;

Or you can simplify it by doing:

var selectedDomainID = lkuDomainType.EditValue ?? string.Empty;

Answer 6

You should use String.IsNullOrEmpty here. Like this:

var selectedDomainID = String.IsNullOrEmpty(lkuDomainType.EditValue) ? string.Empty : lkuDomainType.EditValue;

Equals is a method, you're trying to call a method on a null object which is throwing an exception.

Answer 7

when EditValue is null you cannot call the Equals method on it so the best way to check is to use

lkuDomainType.EditValue == null ? string.Empty : lkuDomainType.EditValue;

Answer 8

The problem is that you are using the object before checking if it's null. You are calling the Equals method of the object, which fails if the reference is null.

You have to exchange your lkuDomainType.EditValue.Equals(null) for lkuDomainType.EditValue == null.

Answer 9

If lkuDomainType.EditValue is null, then "lkuDomainType.EditValue.Equals(someObject)" is the same as coding "null.Equals(someObject)". Well, obviously "null" doesn't have any members or methods (it wouldn't be null if it did). That's why you get a NullReferenceException.

Most of the examples from the other posts will work, including String.IsNullOrEmpty, which is a method that returns a boolean value.