/* (non-Javadoc)
  * @see org.eclipse.californium.core.server.resources.Resource#add(org.eclipse.californium.core.server.resources.Resource)
  */
 @Override
 public synchronized void add(Resource child) {
   if (child.getName() == null) throw new NullPointerException("Child must have a name");
   if (child.getParent() != null) child.getParent().delete(child);
   children.put(child.getName(), child);
   child.setParent(this);
   for (ResourceObserver obs : observers) obs.addedChild(child);
 }