code: public static String rowIndexListToString(final List<Integer> row) {
  		if (row == null || row.isEmpty()) {
  			return null;
  		}
  
  		StringBuffer index = new StringBuffer();
  		boolean addDelimiter = false;
  
  		for (Integer lvl : row) {
  			if (addDelimiter) {
  				index.append(INDEX_DELIMITER);
  			}
  			index.append(lvl);
  			addDelimiter = true;
  		}
  
  		return index.toString();
  	}
docs: Convert the row index to its string representation.
  
  @param row the row index
  @return the string representation of the row index