How to insert blank data in access db

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VB

Hi Everyone,

I have an application in which i have to take reports of the transaction done on particular date range
For this I am creating one temp table in which data is inserted and fetched during form load, here is the code

Dim InDate As String
               Dim OutDate As String
               Dim DtIn As Date
               Dim DtOut As Date
For i As Integer = 0 To ds.Tables(0).Rows.Count - 1
                        Regno = ds.Tables(0).Rows(i)(0).ToString()
                        barcode = ds.Tables(0).Rows(i)(1).ToString()
                        vehityp = ds.Tables(0).Rows(i)(2).ToString()
                        vehimodl = ds.Tables(0).Rows(i)(3).ToString()
                        InDate = ds.Tables(0).Rows(i)(4).ToString()
                        OutDate = ds.Tables(0).Rows(i)(5).ToString()
                        DtIn = DateTime.Parse(InDate)
                        DtOut = DateTime.Parse(OutDate)
                        diff = DtIn - DtOut
                        DiffD = diff.Days
                        DiffH = diff.Hours
                        DiffM = diff.Minutes
                        Try
                            sqlcmd = "Insert Into tmp ([RegistrationNo],[Barcode],[VehicleType],[VehicleModel] , [TranInDate], [TranOutDate], [OutDays], [OutHours], [OutMins]) Values ('" _
                            + Regno + "','" + barcode + "','" + vehityp + "','" + vehimodl + "', '" + InDate.ToString() + "', '" + OutDate.ToString() + "', " + DiffD.ToString() + ", " + DiffH.ToString() + ", " + DiffM.ToString() + ")"
                            cmd.CommandText = sqlcmd
                            cmd.ExecuteNonQuery()
                        Catch ex As Exception
                            MsgBox(ex.Message, "Messageinst")
                        End Try
                    Next

When My InDate is blank it is showing an error as
"String was not recognised as a valid DateTime"

Can anyone help me on how to insert the blank InDate value