How to insert null or empty date from datagridview column to database using vb.net?

Hello fellow coders. I'm asking for your help on how to insert or save empty date value or null value from datagridview column to access database. I research over the web but unfortunately not solved my problem. I'm trying to set dateret as string but it says: "String cannot be converted to date". If I set dateret as Date, then it says: "Not recognized as valid datetime" or "Datatype mismatched". How to address this problem? Following is my simple code. Thank you.

Code:

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Dim connstring As String
            connstring = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=retirement.accdb"
            Dim conn As OleDbConnection = New OleDbConnection(connstring)
            Dim ln, fn, mn, retiredate As String
            'Dim dateret as Date
            'Dim dateret as String

            For i As Integer = 0 To Me.DataGridView1.RowCount - 1

                ln = Me.DataGridView1.Item(0, i).Value
                fn = Me.DataGridView1.Item(1, i).Value
                mn = Me.DataGridView1.Item(2, i).Value
             
             
          If Me.DataGridView1.Item(3, i).Value Is Nothing Or Me.DataGridView1.Item(3, i).Value = String.Empty Then
                'nothing to insert or null value inserted
          else
                  dateretire = Me.DataGridView1.Item(3, i).Value
          End If
             
                Dim Sql = "insert into emprecords(lastname, firstname, middlename, dateretire) values('" & ln & "','" & fn & "','" & mn & "','" & dateret & "')"


                Dim comm As New OleDb.OleDbCommand
                comm.CommandText = Sql
                comm.Connection = conn
                conn.Open()
                comm.ExecuteNonQuery()

                comm.Dispose()
                conn.Close()

            Next
            MsgBox("Imported Successfully! Click refresh button to reload data.", MsgBoxStyle.Information, "Import")
            Me.Close()
        End If

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It's so painful seeing people purposely make their lives difficult and then asking how to fix it. If you do it properly in the first place then there's nothing to fix. Create a DataTable with the appropriate schema, either by calling Fill or FillSchema on a data adapter or just building it manually. Bind that DataTable to your grid, preferably via a BindingSource. Any changes the user makes in the grid will automatically be propagated to the DataTable. You then simply call Update on your data adapter and the data is saved. The DataTable already contains the data, including NULL values where appropriate, so there's nothing to do.

Quote:

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Originally Posted by jmcilhinney

It's so painful seeing people purposely make their lives difficult and then asking how to fix it. If you do it properly in the first place then there's nothing to fix. Create a DataTable with the appropriate schema, either by calling Fill or FillSchema on a data adapter or just building it manually. Bind that DataTable to your grid, preferably via a BindingSource. Any changes the user makes in the grid will automatically be propagated to the DataTable. You then simply call Update on your data adapter and the data is saved. The DataTable already contains the data, including NULL values where appropriate, so there's nothing to do.

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Thank you so much for your suggestion sir but I cannot do that because the data in datagridview is inserted from MS excel.

That's a non sequitur. There's no reason that you cannot populate a DataTable with that data. You can even use a data adapter to retrieve the data from your Excel file straight into a DataTable.