code: public Parent getParent() {
          Node rootNode = getRootNode();
          if (rootNode == null) {
              throw new NullPointerException("The root node is null");
          }
          if (!(rootNode instanceof Parent)) {
              throw new IllegalStateException("The root node of this view is not a Parent");
          }
          return (Parent) rootNode;
      }
docs: Usefull helper method that returns the root node (see {@link #getRootNode()}) as a {@link Parent} if the root node
  extends {@link Parent} or throws an runtime exception. This can be used to simply add a {@link AbstractFXMLViewController}
  based view to a scene that needs a {@link Parent} as a root node.
  
  @return the root node