I found what I believe to be a bug in the JBoss 5.0 Beta 4 distribution, discovered in attempting to migrate our current web application from JBoss 4.2.1.

On deployment, I get:
java.lang.IllegalArgumentException: Adding text to an XML document must not be null
at org.dom4j.DocumentFactory.createText(DocumentFactory.java:174)
at org.dom4j.tree.AbstractElement.addText(AbstractElement.java:899)
at org.jboss.wsf.framework.deployment.WebAppGeneratorDeploymentAspect.createWebAppDescriptor(WebAppGeneratorDeploymentAspect.java:164)
... (rest of stack trace clipped for brevity)

JBoss seems to take offense at something in the dom4j library, which is included in the JBoss distribution. As I said, the web application works properly in 4.2.1. I suspect the XML library is relatively rarely used, so this has escaped detection. Thanks.