I am have created a Java Webservice application which uses JAXB. When I test my application using SoapUI and I send a SOAP message like `<foo></foo>`, it will convert to `0`, but if there's no `<foo>` tag in my SOAP message, it will convert to `null`. Why is `<foo></foo>` not converted to `null`? How can I change it?

```
@WebMethod
public void test(Integer foo) {
    System.out.print(foo);
}

```