Error: New is not valid in this context and optional parameters must specify a default value in VB.Net

Dear Sir,

I'm trying convert C# to vb.net but I have an error like this : `New' is not valid in this context and optional parameters must specify a default value in VB.Net`

Please guide me

Thanks

Code in C#

class testcode
{
    public Control Content { get; }
    public void Show(Control opener, Size preferredSize = new Size())
    {

    }
}

 Code in VB.NET

Public Class testcode
    Public ReadOnly Property Content As Control

`Error below line code
    Public Sub Show(ByVal opener As Control, Optional ByVal preferredSize As New Size())

	End Sub

End Class