code: @Override
  	public final Object getValueAt(final int row, final int col) {
  		TableTreeNode rowNode = getNodeAtLine(row);
  		return getValueAt(rowNode, col);
  	}
docs: Retrieves the value at the given row and column. This implementation delegates to
  {@link #getValueAt(TableTreeNode, int)}, which subclasses must implement.
  
  @param row the row index
  @param col the column index.
  @return the value for the specified cell.