Filter expression '1' does not evaluate to a Boolean term

public DataSet Fill_Dataset()
    {
        DataSet ds = new DataSet();

        con = new SqlConnection(str);
        con.Open();
        cmd = new SqlCommand("sp_new", con);
        cmd.CommandType = CommandType.StoredProcedure;
        SqlDataAdapter da = new SqlDataAdapter(cmd);
        da.Fill(ds);

        DataView dv = ds.Tables[1].DefaultView;

        if(ds.Tables[0].Rows.Count>1)
        {
            for (int i = 0; i < ds.Tables[0].Rows.Count;i++ )
            {
                DataRow dr = ds.Tables[0].Rows[i];
                DataTable dt1;
                dv.RowFilter=dr["country_id"].ToString();
                dt1 = dv.ToTable();
                ds.Tables.Add(dt1);
            }
        }
        return ds;
}

protected void excel_generation_Click(object sender, EventArgs e)
    {
        try
        {
            Export_Excel();
        }
        catch (Exception ex)
        {
            throw ex;
        }
    }

    void Export_Excel()
    {
        con = new SqlConnection(str);
        con.Open();
        DataSet ds = Fill_Dataset();

        using (XLWorkbook wb = new XLWorkbook())
        {
            wb.Worksheets.Add(ds);
            wb.Style.Alignment.Horizontal = XLAlignmentHorizontalValues.Center;
            wb.Style.Font.Bold = true;
            Response.Clear();
            Response.Buffer = true;
            Response.Charset = "";
            Response.ContentType = "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet";
            Response.AddHeader("content-disposition", "attachment;filename=Summary_Rpt.xlsx");

            using (MemoryStream MyMemoryStream = new MemoryStream())
            {
                wb.SaveAs(MyMemoryStream);
                MyMemoryStream.WriteTo(Response.OutputStream);
                Response.Flush();
                Response.End();
            }
        }
    }