Is there way to have an optional parameter which has a default of a class?

I have this declared function and I would like toApplication to be optional but would default to the Framework.App class.

    Public Shared Function Encrypt(ByVal tcString As String, ByVal tcKey As String, _
     Optional ByVal toApplication As Object = "") As Boolean

If I try the following, it gives an error:

    Public Shared Function Encrypt(ByVal tcString As String, ByVal tcKey As String, _
     Optional ByVal toApplication As Framework.App = New Framework.App) As Boolean

The error is "Constant expression is required".