DATACMNS-1762 - Support Optional wrapping for projection getters

[mp911de]

We now support nullable wrappers for projection interfaces. Getters are inspected whether their return type is a supported nullable wrapper. If so, then the value can be wrapped into that type. Null values default in that case to their corresponding empty wrapper representation.

class Customer {

	Long id;
	String firstname, lastname;
	Address address;
}

interface CustomerProjection {

	Optional<String> getFirstname();

	Optional<AddressExcerpt> getAddress();
}


Customer customer = new Customer();
customer.firstname = "Walter";

CustomerProjection projection = …;

assertThat(projection.getFirstname()).hasValue("Walter");


customer.firstname = null;
assertThat(projection.getFirstname()).isEmpty();

Also, extracted NullableWrapperConverters from QueryExecutionConverters and removed ReactiveWrappers from QueryExecutionConverters .

---

We should reconsider the package for NullableWrapperConverters as further extensions (Iterable -> Streamable) might be future enhancements.

Related ticket: DATACMNS-1762
Previous pull request: #457.

[wimdeblauwe]

Interesting test! Did not think about this use case 👍

[wimdeblauwe]

This is probably an exact copy of QueryExecutionConverters.WrapperType. Shouldn't this be refactored to use the same class? Or is that not possible for backwards-compatibility reasons?

[mp911de]

We don't really want to expose this type so it makes sense to make it package-private. We'd rather go for a duplication really as nullable wrappers and result wrappers (Page, Seq, CompletableFuture) touch different concepts which follow a similar structure but they aren't the same.

[wimdeblauwe]

Ok, clear! Looking forward to using this in a future release :-)

[wimdeblauwe]

Thanks for this @mp911de ! I have added 2 remarks above from having a look at what you have done. I could not have done it myself, so I'm very grateful for this 🙇