role-hint and configuration generated with empty values

as reported on mavendev, descriptor generated from java 5 annotations is different from descriptor generated from javadoc tags:

• phase is always added without value
• elements within <configuration> have an explicit closing tag if there's no content (was a compressed tag like <foo implementation="a.b.C"/>)
• role-hint-tag with empty content is added if there's no role-hint (wasn't there, IIRC this could be an issue)

this is probably due to the fact that annotations are defined with empty String default value where javadoc tags have no default value then null