src/main/java/com/workplacesystems/utilsj/collections/TransactionalBidiTreeMap.java
private static <K,V> Node<K,V> getParent(final Node<K,V> node, final int index) {

        return ((node == null)
                ? null
                : node.getParent(index));
    }
private static <K,V> Node<K,V> getParent(final Node<K,V> node, final int index) {

        return ((node == null)
                ? null
                : node.getParent(index));
    }
get a node's parent. mind you, the node, or its parent, may not
exist. no problem

@param node the node (may be null) in question
@param index KEY or VALUE