Nullable type and if issue

Question

Here is simplest piece of code

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


        

Answer 1

It's because you're using the 3-argument form of If(). It will try to return the same type based on parameters 2 and 3, so the Nothing in parameter 2 gets converted to a DateTime (and you get DateTime.MinValue).

If you use the 2-argument form, it applies null-coalescing, i.e. when the first argument (which must be an Object or a nullable type) is Nothing, it returns the second argument, otherwise it returns the first argument.

If you use Dim foo As DateTime? = If(Nothing, new DateTime(2018, 3, 20)) you will get the expected value.