JAXB gives me: java.lang.IllegalArgumentException: is parameter must not be null

I am doing using JAXB to unmarshall some XML into Java objects:

My code looks a little like this:

InputStream testMsg = getClass().getResourceAsStream("TestDocumentEvent.xml");
Unmarshaller unmarshaller = JAXBContext.newInstance(DocumentEvent.class).createUnmarshaller();
DocumentEvent unmarshalled = (DocumentEvent) unmarshaller.unmarshal(testMsg);

However, when I run this code I get an exception:

java.lang.IllegalArgumentException: is parameter must not be null

What's going on?

From stackoverflow

• This is because the InputStream you are passing to the unmarshaller ('is' parameter, geddit) is null, check that the resource name is correct.

  SCdF : I know, I answered my own question. I added this because there isn't much on google about this and the error isn't that readable

  Jon Skeet : I don't know, it seems pretty obvious to me - if the unmarshal call is complaining immediately that its argument is null, what's unreadable about that?

  Eddie : You are saying that "IS" is short for "InputStream" in the complaint? Yes, that's a little unclear, but at least from context it's easy to figure out.

  SCdF : @Jon, if the world was made of Jon Skeets we wouldn't need SO, if your rep is anything to go by. Sadly marginal code jockeys such as myself still need a helping hand once and awhile.