How I can save the record of new added row of grid view with respect to hidden field if hidden field id is empty I want to save that record

<asp:GridView ID="grdParticular" runat="server" ShowHeaderWhenEmpty="true" EmptyDataText="No data in gridview" Visible="true" CssClass="table table-striped table-bordered" ShowFooter="True" ShowHeader="true" AutoGenerateColumns="False" DataKeyNames="particula_id">
                    <columns>

                        <asp:TemplateField HeaderText="ID" Visible="false">
                            <itemtemplate>
<asp:HiddenField runat="server" ID="ParID" Value='<%# Eval("particula_id")%>' />
                            
                        


                        <asp:TemplateField HeaderText="Particular">
                            <itemtemplate>
     <asp:TextBox ID="txtPArticular" Text='<%# Eval ("par")%>' runat="server">
                            
                        
                        <asp:TemplateField HeaderText="Result">
                            <itemtemplate>
                                <asp:TextBox ID="txtResult" Text='<%# Eval ("result")%>' runat="server">
                            
                        
                        <asp:TemplateField HeaderText="Unit">
                            <itemtemplate>
                                <asp:TextBox ID="txtUnit" runat="server" Text='<%# Eval ("unit")%>'>
                            

                        
                        <asp:TemplateField HeaderText="Value">
                            <itemtemplate>
                                <asp:TextBox ID="txtValue" runat="server" Text='<%# Eval ("value")%>'>
                            
                        


                        <asp:templatefield>
                            <itemtemplate>
                                <asp:Button ID="ButtonAddNewRow" runat="server" Text="Add Row" OnClick="ButtonAddNewRow_Click" />

protected void ButtonAddNewRow_Click(object sender, EventArgs e)
        {
            int rowIndex = 0;
            if (ViewState["datatable"] != null)
            {
                DataTable dtCurrentTable = (DataTable)ViewState["datatable"];
                DataRow drCurrentRow = null;
                if (dtCurrentTable.Rows.Count > 0)
                {
                    for (int i = 1; i <= dtCurrentTable.Rows.Count; i++)
                    {
                        //extract the TextBox values
                        TextBox box1 = (TextBox)grdParticular.Rows[rowIndex].Cells[1].FindControl("txtPArticular");
                        TextBox box2 = (TextBox)grdParticular.Rows[rowIndex].Cells[2].FindControl("txtResult");
                        TextBox box3 = (TextBox)grdParticular.Rows[rowIndex].Cells[3].FindControl("txtUnit");
                        TextBox box4 = (TextBox)grdParticular.Rows[rowIndex].Cells[4].FindControl("txtValue");

                        drCurrentRow = dtCurrentTable.NewRow();
                        //drCurrentRow["RowNumber"] = i + 1;

                        dtCurrentTable.Rows[i - 1]["par"] = box1.Text;
                        dtCurrentTable.Rows[i - 1]["Result"] = box2.Text;
                        dtCurrentTable.Rows[i - 1]["Unit"] = box3.Text;
                        dtCurrentTable.Rows[i - 1]["Value"] = box4.Text;
                        rowIndex++;
                    }
                    dtCurrentTable.Rows.Add(drCurrentRow);
                    ViewState["datatable"] = dtCurrentTable;

                    grdParticular.DataSource = dtCurrentTable;
                    grdParticular.DataBind();
                }
            }
            else
            {
                Response.Write("ViewState is null");
            }
}