Evaluating the example request (xacmlEmptyAttributeRequest.xacml) against the example policy (policy-empty-attributes.xacml) results in a null pointer exception on line 203 of org.herasaf.xacml.core.policy.impl.AttributeDesignatorType.
I would expect the empty AttributeValue to unmarshal to an empty string as attribute value content for two reasons:
The attribute designators give a null pointer exception (as described)
String manipulation functions expect string attributes to not be null
It is not clear how an empty string would otherwise be marshalled than as an empty attribute.