carry on from the last question the "selectpicturedialog", i now faced another problem.

I have a picturebox which display photo which i selected in the dialog, i save the image path to a sql database along with some other data.
it all save & load fine from the database.
then i went on and test to save no image in the picturebox and just the text data. so , in the database image column is "null", it saved well. but i can not load it. it gave me an error.

here my code: the red part causes the problem

Code:
 Private Sub FoodjournalDataGrid_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles FoodjournalDataGrid.Click
        Dim currentrow As Integer = FoodjournalDataGrid.CurrentRowIndex
        Dim img As String

        If FoodjournalDataGrid.VisibleRowCount <> 0 Then
            DateTimePicker1.Value = FoodjournalDataGrid.Item(currentrow, 0)
            TextBox1.Text = FoodjournalDataGrid.Item(currentrow, 1)
            img = FoodjournalDataGrid.Item(currentrow, 2)
            If img = String.Empty Then
                PictureBox1.Image = Nothing
            Else
                PictureBox1.Image = New Bitmap(img)
            End If
        Else
            MsgBox("No record found")
        End If
        FoodjournalDataGrid.Visible = False
    End Sub