Method not found for
required = false when working on a Maven based project in IntelliJ IDEA 12.
The following line:
@XmlElementRef(name = "args0", namespace = "http://irt01e.wsbeans.iseries/xsd", type = JAXBElement.class, required = false)
was marked red.
Classpath ordering was incorrect. IntelliJ put the JDK as the last element and moving it down (at least behind JAX-WS 2.2) solved the problem.
See also: Issue IDEA-60966