Проблема при написании хранимой процедуры SQL

CREATE PROCEDURE [dbo].[sp_empInfo]
@empID int =null, 
@TesterName varchar(250)=null
as 
declare @strSql nvarchar(4000)

			SET	@strSql='Declare  users_cursor CURSOR FOR SELECT ID,TesterName FROM emp Where Status=1 '
				IF @empID IS NOT NULL AND LEN(@empID) > 0
					SET	@strSql = @strSql +' AND ID='+CAST(@empID AS NVARCHAR(10))
				IF @TesterName IS NOT NULL AND LEN(@TesterName) > 0
					SET	@strSql = @strSql +' AND TesterName='+@TesterName
		exec sp_executesql @strSql
   		open   users_cursor
				fetch next from users_cursor into @empID, @TesterName
						while @@FETCH_STATUS = 0 BEGIN
						---PROCESS
			    fetch next from users_cursor into @empID, @TesterName
	 	END
	 	close users_cursor
		deallocate users_cursor  

when i pass TesterName as Nil I'm getting Error 
Invalid column name 'Nil'