When to check for nulls

Question

This is kinda an open ended question but I'm trying to sharpen my skills with good practices in exception handling specifically when to check for nulls in general.

I know mostly when to check for nulls but I have to say half the time I don't and that's bothering to me. I know ints cannot be set to null unless you use a nullable int. I know strings can be set to null OR empty hence you can check for IsNullOrEmpty.

Obviously in constructors you want to add your explicit checks there also. That's a given. And that I think you should check for null anytime you're passing in an array, generic object, or other objects into a method that can be set to null basically right?

But there is more here to exception handling. For instance I don't know when to always check and throw a null ref exception explicitely in code. If I've got incoming params, usually it's pretty straight forward but there are always cases where I ask myself, is an explicit null throw needed?

I don't really have specific examples but wondering if there's a good reference out there that really talks about exception handling in reference to when to throw them (inside methods, classes, you name it).

Answer 1

You shouldn't throw NullReferenceException. If it is an argument that is null throw ArgumentNullException instead.

I prefer to check for null for all reference types parameters of public/protected methods. For private methods, you may omit the check if you're sure all calls will always have valid data.