code: @Override
    final protected void addRangeEmpty(int left, int right, int additionalId,
        long additionalRef) {
      String key = left + "_" + right;
      if (index.containsKey(key)) {
        // do nothing (empty...)
      } else {
        root = addRange(root, left, right, additionalId, additionalRef, null,
            null);
        root.color = MtasRBTreeNode.BLACK;
      }
    }
docs: /*
  (non-Javadoc)
  
  @see mtas.codec.tree.MtasTree#addRangeEmpty(int, int)