code: void unregisterEntry(ListIterator<PathElement> iterator, ConcreteNotificationHandlerRegistration.NotificationHandlerEntry entry) {
          if (!iterator.hasNext()) {
              // leaf node, unregister the entry here
              entries.remove(entry);
              return;
          }
  
          PathElement element = iterator.next();
          final NotificationHandlerNodeSubregistry subregistry = children.get(element.getKey());
          if (subregistry == null) {
              return;
          }
          subregistry.unregisterEntry(iterator, element.getValue(), entry);
  
      }
docs: Unregister the entry from here (if the registry is the leaf node) or continue to traverse the tree