Using 'null' as an EJB-QL parameter possible?

[hoagiex]

I'm building a tree structured Object model. I.o.w. there a single POJO (ResourceEJB) with a parent reference (Many to One) and a collection of child references (One to Many) which are of the same type.

I have a method which determines all ResourceEJB object that share a certain ResourceEJB parent:

 public Collection<ResourceEJB>
 findByParentID(Long aParentID)
 throws DAOException
 {
 try
 {
 ResourceEJB myParent = null;
 if(aParentID != null)
 myParent = (ResourceEJB)findByID(aParentID);

 return theManager.createQuery(
 "from ResourceEJB resource where resource.parent = :parent")
 .setParameter("parent", myParent).getResultList();
 }
 catch(Exception anException)
 {
 throw new DAOException(anException);
 }
 }

The problem is that I can't find the 'root' Node, which has a parent value of 'null'. How can I retrieve an Object using EJB-QL on a parameter which has a null value?

[mooktarus]

if( aParentId == null ) {
 return theManager.createQuery(
 "from ResourceEJB resource where resource.parent IS NULL")
 .getResultList();
}