Excelで選択範囲に対し、表示上空欄に見える値をクリアして本当の空欄にする

gistfile1.vb

Sub Macro1()
    Dim i As Long
    For i = 1 To Selection.Count
        If Not IsEmpty(Selection(i)) Then
            If Selection(i).Value = "(NULL)" Or _
                Asc(Selection(i)) = -31871 Or _
                Asc(Selection(i)) = 63 Then
                Selection(i).ClearContents
            End If
        End If
    Next i
End Sub