how to bind gridview item template to DB stored procedure?

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SQL-Server

SQL-Server-2008

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Hi.

I have a gridview and inside the gridview there is a templated field , so i want to bind the lable of this templated field(item template) to the stored procedure in the sqlserver , and to change the lable text to what is selected from stored procedure .
here is the stored procedure :

ALTER PROCEDURE [dbo].[Get_LastIdHowzeEducationFinishDate_SP]
AS
BEGIN 
select he.FinishLevelDate as 'تاریخ اتمام سطح'
       from PersonHowEducation prh inner join HowzeEducation he on 
              prh.HowzeEducationId=he.HowzeEducationId
              where prh.IdCode=
              (Select IdCode from Persons where IdCode=IDENT_CURRENT('persons'))
END

and this is the code for calling stored procedure and to show it inside lable(item template):

DataTable dt1 = DataProvider.ExecuteDataTable("[dbo].[Get_LastIdHowzeEducationFinishDate_SP]", CommandType.StoredProcedure);
GridView1.FindControl("Label1").DataBind();

but this exception appears:
Object reference not set to an instance of an object
how can i do that?