How to span a column in a PdfDocument by using the PdfLightTable?

// Create a new instance of PdfDocument class.
PdfDocument document = new PdfDocument();
// Add a page to the document.
PdfPage page = document.Pages.Add(); 
//Create pdfLightTable.
PdfLightTable table = new PdfLightTable();
// Set the database into pdflighttable source. 
table.DataSource = CreateTable();
// Call the row events.
table.BeginRowLayout += new BeginRowLayoutEventHandler(table_BeginRowLayout);
// Draw the table into page.
table.Draw(page, new PointF(0, 0));          
// Save and close the document.
document.Save("Sample.pdf");
document.Close(true);
//Row event method.
private void table_BeginRowLayout(object sender ,BeginRowLayoutEventArgs args)
{
if (args.RowIndex == 0 || args.RowIndex == 4)
{                
int[] span=new int[2]; //Array length is table.column count. 
span[0] = 2;
args.ColumnSpanMap = span;
}
}