Bug 136740 Error exporting data from a grouped report.
data/org.eclipse.birt.data/src/org/eclipse/birt/data/engine/impl/ExprManagerUtil.java
for ( int i = 0; i < source.length; i++ )
		{
			source[i] = (Node) result.get( i );
		}
		validateNodes( source );
	}
	/**
	 * 
	 * @param source
	 * @return
	 * @throws DataException 
	 */
	private static void validateNodes( Node[] source ) throws DataException
	{
		Node[] preparedNodes = populateNodeList( source );
		for ( int i = 0; i < preparedNodes.length; i++ )
		{
			isValidNode( preparedNodes[i], preparedNodes[i] );
		}
	}
	/**
	 * 
	 * @param startNode
	 * @param candidateNode
	 * @return
	 * @throws DataException 
	 */
	private static void isValidNode( Node startNode, Node candidateNode ) throws DataException
	{