Should a API throw NullPointerExceptions

Question

I use a commerical API and had a NullpointException coming from the API code.

The support tells me that it is expected because one of the input-parameters of the method I called was null and this parameter is needed to use the methdod.

Is this really my fault because I haven't checked the parameters before passing them to the API?

Isn't it bad practice to let NullpointerExceptions out of your API? If not I would have to check for all kind of RuntimeExceptions if I use a method of that API if I want to make sure my software doesn't crash.

If it is bad practice, are there any documents or specifications which refer to this?

Answer 1

Yeah, I would say they should throw IllegalArgumentException

See: IllegalArgumentException or NullPointerException for a null parameter?

And do read on, because this is the best answer: https://stackoverflow.com/a/47710/2586804

The main difference is IllegalArgumentException makes it explicit that you have made a mistake when using the library.

Either way, you just need to use the library correctly. And only catch exceptions if you can handle them.

Answer 2

You say that you would have to check for all RuntimeExceptions. The answer to that is no! It's OK for an API to throw unchecked runtime exceptions (regardless if it's a NullPointerException, a IllegalArgumentException or something else) in case it is used the wrong way.

In your case you use the API the wrong way, so you get a NullPointerException. If you want to catch that, how would your code look like?

try {
    useAPI();
} catch(NullPointerException e) {
    useAPIcorrectly();
}

Why not make that just useAPIcorrectly();? ;-)

You could put some debuging output in the catch block for development but the again: If in development, the stack trace of a NullPointerException is also sufficient for debugging. You would then fix it to the correct API use and never see those exceptions again :-)