[Solved] ASP.Net Error: NpgsqlCommand AddWithValue is not member of Npgsql.ParameterCollection

ASP.Net error NpgsqlCommand AddWithValue is not member of Npgsql.ParameterCollection

   Public Class GraphData
        Public Property label As String
        Public Property value As Integer
    End Class

    <WebMethod()>
    Public Shared Function GetGraphData(ByVal customerId As String) As List(Of GraphData)
        Dim graphDataList As List(Of GraphData) = New List(Of GraphData)()
        Dim constr As String = ConfigurationManager.ConnectionStrings("constr").ConnectionString
        Dim con As NpgsqlConnection = New NpgsqlConnection(constr)
        Dim cmd As NpgsqlCommand = New NpgsqlCommand("SELECT TOP 10 CAST(OrderDate AS DATE) OrderDate, SUM(Freight) Freight FROM  Orders GROUP BY Orderdate")
        cmd.Parameters.AddWithValue("@Id", If(Not String.IsNullOrEmpty(customerId), customerId, CObj(DBNull.Value)))
        cmd.Connection = con
        con.Open()
        Dim sdr As NpgsqlDataReader = cmd.ExecuteReader()
        While sdr.Read()
            graphDataList.Add(New GraphData() With {
                .label = Convert.ToString(sdr("OrderDate")),
                .value = (Convert.ToInt32(sdr("Freight")))
            })
        End While
        con.Close()

        Return graphDataList
    End Function

Aspx code:-

    <link type="text/css" rel="stylesheet" href="//cdnjs.cloudflare.com/ajax/libs/morris.js/0.5.1/morris.css">
    <script type="text/javascript" src="//ajax.googleapis.com/ajax/libs/jquery/1.9.0/jquery.min.js"></script>
    <script type="text/javascript" src="//cdnjs.cloudflare.com/ajax/libs/raphael/2.1.0/raphael-min.js"></script>
    <script type="text/javascript" src="//cdnjs.cloudflare.com/ajax/libs/morris.js/0.5.1/morris.min.js"></script>
    <script type="text/javascript">
        $(document).ready(function () {
            $.ajax({
                type: 'POST',
                url: "Chart_test.aspx/GetGraphData",
                dataType: 'json',
                contentType: "application/json; charset=utf-8",
                data: {},
                success: function (result) {
                    new Morris.Donut({
                        element: 'line-chart',
                        data: result.d,
                        xkey: 'label',
                        ykeys: ['value'],
                        labels: ['value']
                    });
                },
                error: function (error) {
                    alert(error.responseText);
                }
            });
        });
    </script>

    <div id="line-chart">
    </div>