Nullable type and if issue

Question

Here is simplest piece of code

Dim testInvoiceDate As DateTime? = If(String.IsNullOrEmpty(Nothing),
                                      Nothing,
                   


        

Answer 1

That compiles in VB.NET(as opposed to C#) because here Nothing has multiple meanings.

1. null
2. default value for that type

In this case the compiler uses the second option since there is otherwise no implicit conversion between the DateTime and Nothing(in the meaning of null).

The default value of DateTime(a Structure which is a value type) is #1/1/0001 12:00:00 AM#

You could use this to get a Nullable(Of DateTime):

Dim testInvoiceDate As DateTime? = If(String.IsNullOrEmpty(Nothing), New Nullable(Of Date), New DateTime(2018, 3, 20))

or use an If:

Dim testInvoiceDate As DateTime? = Nothing
If Not String.IsNullOrEmpty(Nothing) Then testInvoiceDate = New DateTime(2018, 3, 20)