code: @Override
      public Node getChildNode(String childNodeId)
      {
          NodeLink link = new NodeLink(getNodeId(), childNodeId);
  
          if (this.children == null)
          {
              return null;
          }
          else
          {
              return this.children.get(link);
          }
      }
docs: Retrieves child node of this node for a given child node ID