Asp.net - Get By Reflection The Value Of A Property Whose Getter Has An Optional Value

I am retrieving several properties of a control. Here is how I used to retrieve properties (with pinfo of type PropertyInfo):

value = pinfo.GetValue(obj, nothing)

That worked well, but now I am facing a property that has a optional value, and I get an error message telling me that the number of parameters is incorrect. So I changed my code by this one:

Dim index As Object() = {Nothing}
value = pinfo.GetValue(obj, index)

At this point, I didn't get any error message, but this code doesn't retrieve the good value. It only works if I replace Nothing by the default value provided by the property accessor...

But I don't know in advance what this default value is! And this code is within a function that retrieves properties that doesn't have optional values, so I cannot change the code especially for one case or another..

I am working on .NET 2.0

EDIT: More precisions about the case leading to the problem

Here is an example of property leading to the problem:

ReadOnly Property Foo(Optional ByVal Number As Integer = -1) As String
Get
If Number = -1 Then

[Code]....

With this kind of property, none of the codes above retrieve the good string.

My best guess would be to try the first code for general purposes, catch the appropriate exception, and then dynamically retrieve the default value of the parameter (Number in that case) and its type, so that I can call getValue with this default value.

So, How can I retrieve the default value of the optional parameter?