docs: protected final NodeIterator referringNodes( ReferenceType referenceType ) throws RepositoryException {
          if (!this.isReferenceable()) {
              return JcrEmptyNodeIterator.INSTANCE;
          }
  
          // Get all of the nodes that are referring to this node ...
          Set<NodeKey> keys = node().getReferrers(sessionCache(), referenceType);
          if (keys.isEmpty()) return JcrEmptyNodeIterator.INSTANCE;
          return new JcrNodeIterator(session(), keys.iterator(), keys.size(), null);
      }