code: protected void addNode( Node nodeToInsert, Node insertBeforeNode )
      {
          // Insert node.
          nodeToInsert.next = insertBeforeNode;
          nodeToInsert.previous = insertBeforeNode.previous;
          insertBeforeNode.previous.next = nodeToInsert;
          insertBeforeNode.previous = nodeToInsert;
      }
docs: Inserts a new node into the list.
  
  @param nodeToInsert  new node to insert
  @param insertBeforeNode  node to insert before
  @throws NullPointerException if either node is null