A CTE request creates an error in a dataset using C # for webform in asp.net

RESOLVED ..

This was allowed as I was making a stupid mistake. I did not initialize the String Builder StringBuilder sb = new StringBuilder ();

I am using the following CTE request on my website to retrieve data using C #. But it gives an error in the if statement inside the loop

ERROR MESSAGE

The System.NullReferenceException was not handled by the user code Message = The object reference was not installed in the object instance.

    String strSqlCTE;

    strSqlCTE= " DECLARE @PageId int ";
    strSqlCTE += " SET @PageId =" + pageid + "; ";
    strSqlCTE += " WITH RecursiveTable (PageId, PageName, PageInternalLink, PageInternalLinkUrl, PageInheritance, Level) ";
    strSqlCTE += " AS(SELECT      tt.PageId,  tt.PageName, tt.PageInternalLink, tt.PageInternalLinkUrl, tt.PageInheritance,  0 AS Level ";
    strSqlCTE += " FROM pg_Pages AS tt WHERE PageId = @PageId ";
    strSqlCTE += " UNION ALL ";
    strSqlCTE += " SELECT tt.PageId,  tt.PageName, tt.PageInternalLink, tt.PageInternalLinkUrl, tt.PageInheritance, Level + 1 ";
    strSqlCTE += " FROM pg_Pages AS tt ";
    strSqlCTE += " INNER JOIN RecursiveTable rt ON rt.PageInheritance = tt.PageId  ) ";
    strSqlCTE += " SELECT * FROM RecursiveTable ORDER BY Level DESC ";

    DataSet dsBC = new DataSet();
    dsBC = DataProvider.Connect_Select(strSqlCTE);
    if (dsBC.Tables[0].Rows.Count > 0)
    {
        int RowCount = dsBC.Tables[0].Rows.Count;
        StringBuilder sb = null;
        for ( int i = 0; i <= RowCount; i++)
        {
            if (i == RowCount)
            {
                sb.Append("<a href='" + dsBC.Tables[0].Rows[0]["PageInternalLinkUrl"].ToString() + "'>" + dsBC.Tables[0].Rows[0]["PageName"].ToString().ToUpper() + "</a>");
            }
            else
            {
                sb.Append("<a href='" + dsBC.Tables[0].Rows[0]["PageInternalLinkUrl"].ToString() + "'></a> ● ");
            }

        }

        ltrBreadCrumb.Text = sb.ToString();

    }

My CTE request works, and below is the actual request

DECLARE @PageId int
SET @PageId = 31;
WITH RecursiveTable (PageId, PageName, PageInternalLink, PageInternalLinkUrl, PageInheritance, Level)
AS(
   --Anchor
    SELECT      tt.PageId,  tt.PageName, tt.PageInternalLink, tt.PageInternalLinkUrl, tt.PageInheritance,  0 AS Level
    FROM pg_Pages AS tt
    WHERE PageId = @PageId
    UNION ALL
   --Recursion
    SELECT tt.PageId,  tt.PageName , tt.PageInternalLink, tt.PageInternalLinkUrl, tt.PageInheritance, Level + 1
    FROM pg_Pages AS tt
    INNER JOIN RecursiveTable rt ON rt.PageInheritance = tt.PageId
)
SELECT * FROM RecursiveTable ORDER BY Level DESC

This works well when run in a management studio, but after executing the instruction, generate an error

sb.Append("<a href='" + dsBC.Tables[0].Rows[0]["PageInternalLinkUrl"].ToString() + "'></a> ● ");

dsBC.Tables [0]. Rows.Count . , , , , CTE.

- , , .