An incorrect data node might be added to the network topology, an exception is thrown though

      if (clusterMap.add(node)) {
        LOG.info("Adding a new node: "+NodeBase.getPath(node));
        if (rack == null) {
          numOfRacks++;
        }
        if (!(node instanceof InnerNode)) {
          if (depthOfAllLeaves == -1) {
            depthOfAllLeaves = node.getLevel();
          } else {
            if (depthOfAllLeaves != node.getLevel()) {
              LOG.error("Error: can't add leaf node at depth " +
                  node.getLevel() + " to topology:\n" + oldTopoStr);
              throw new InvalidTopologyException("Invalid network topology. " +
                  "You cannot have a rack and a non-rack node at the same " +
                  "level of the network topology.");
            }
          }
        }