DataReader - dr.IsDBNull(i)

Try
            ' Open a connection.
            cn.Open()
            dr = cmd.ExecuteReader()

' Display all fields
            Do While dr.Read
                Dim res As String = ""
                Dim i As Integer
                ' Iterate over all fields.
                For i = 0 To dr.FieldCount - 1
                    ' Insert a comma if necessary.
                    If res.Length > 0 Then res &= ", "
                    ' Append field name and value.
                    res &= dr.GetName(i) & "="
                    If dr.IsDBNull(i) Then
                        res &= "<NULL>"
                    Else
                        res &= dr.GetValue(i).ToString
                    End If
                Next
                ' Append to the result textbox.
                txtOut.AppendText(res & ControlChars.CrLf)
            Loop
            dr.Close()

Catch ex As OleDbException
            Debug.WriteLine(ex.Message)
        Finally
            ' Close the connection.
            cn.Close()
        End Try

Try
' Open a connection.

cn.Open()
dr = cmd.ExecuteReader()

' Display all fields

Do While dr.Read
Dim res As String = ""
Dim i As Integer
' Iterate over all fields.

For i = 0 To dr.FieldCount - 1
' Insert a comma if necessary.

If res.Length > 0 Then res &= ", "
' Append field name and value.

res &= dr.GetName(i) & "="
If dr.IsDBNull(i) Then
res &= "<NULL>"
Else
res &= dr.GetValue(i).ToString
End If
Next
' Append to the result textbox.

txtOut.AppendText(res & ControlChars.CrLf)
Loop
dr.Close()

Catch ex As OleDbException
Debug.WriteLine(ex.Message)
Finally
' Close the connection.

cn.Close()
End Try