Null value issue writing to my database

Hi,
I am looking at someone code and need to fix an Null issue. It is really simple but i have not worked in .NET in awhile.
I have a function that takes the values that have been entered into a grid are then written to my sql database.
i need to make sure that if there is a null value, to set it to "" or not null before writing it away
So in belows code snippet, i need to test the PortfolioDescription before getting written tot eh database

thanks allot :)

below is the code
can i use the isDBNull function?

        Dim da As New OdbcDataAdapter
        Dim cmd As New OdbcCommand
        Dim cmd_del As New OdbcCommand
        Dim cmd_ins As New OdbcCommand
        Dim cn As New OdbcConnection
        Dim pr, pr2, pr3 As OdbcParameter

        With cn
            .ConnectionString = CON_STR
            Try
                .Open()
            Catch ex As Exception
                ErrorRoutine(ex)
            End Try
        End With

        With cmd
            .Connection = cn
            .CommandText = " UPDATE ClientGroupPortfolio" & _
                           " SET PortfolioCode=?,PortDescription=?,ExReport=?" & _
                           " WHERE GroupID=? AND PortfolioCode=?"

            '.Parameters.Add("@GroupID", OdbcType.VarChar, 4, "GroupID")
            .Parameters.Add("@PC", OdbcType.VarChar, 6, "PortfolioCode")
            .Parameters.Add("@PDesc", OdbcType.Char, 50, "PortDescription")
            .Parameters.Add("@ExRpt", OdbcType.Bit, 1, "ExReport")

            pr = .Parameters.Add("@GroupID", OdbcType.VarChar, 4, "GroupID")
            pr.SourceVersion = DataRowVersion.Original
            pr2 = .Parameters.Add("@PortfolioCode", OdbcType.VarChar, 6, "PortfolioCode")
            pr2.SourceVersion = DataRowVersion.Original
         
           
        End With

        With cmd_ins
            .Connection = cn
            .CommandText = " INSERT INTO ClientGroupPortfolio" & _
                           " (GroupID,PortfolioCode,PortDescription,ExReport)" & _
                           " VALUES(?,?,?,?)"
            .Parameters.Add("@GroupID", OdbcType.VarChar, 4, "GroupId")

            .Parameters.Add("@PortfolioCode", OdbcType.VarChar, 6, "PortfolioCode")
            .Parameters.Add("@PortDescription", OdbcType.Char, 50, "PortDescription")
            .Parameters.Add("@ExReport", OdbcType.Bit, 1, "ExReport")

        End With


        da.UpdateCommand = cmd
        da.DeleteCommand = cmd_del
        da.InsertCommand = cmd_ins
        Try
            da.Update(dtCGP)
            MessageBox.Show("Updates Completed!", "Client Reporting Group Maintenance", MessageBoxButtons.OK, MessageBoxIcon.Information)
            Exit Sub
        Catch ex As Exception
            MessageBox.Show("Update Failed! " & ex.Message, "Client Reporting Group Maintenance", MessageBoxButtons.OK, MessageBoxIcon.Exclamation)
            'ErrorRoutine(ex)
        End Try

        cn.Close()