`Optional.empty()` not excluded if property declared with type `Object`

[jearton]

Jackson version is 2.6.6
Here is the code:

        ObjectMapper mapper = new ObjectMapper();
        mapper.setSerializationInclusion(JsonInclude.Include.NON_ABSENT);
        mapper.registerModule(new Jdk8Module());

        JsonResult result = new JsonResult();
        result.setA(Optional.empty());
        result.setB(Optional.empty());
        System.out.println(mapper.writeValueAsString(result));

@Data
public class JsonResult {
    private Object a;
    private Optional<Object> b;
}

Then I got the output: {"a":null}

The real value of both is the same, why the results are different?

How can I avoid null in such case?

By the way, I tried 'NON_EMPTY'. It can work, but it also ignores zero and empty array. I want to keep them.

[cowtowncoder]

Please use mailing list for usage question; issue tracker is for reporting bugs.

[cowtowncoder]

As to the question however: perhaps this is a bug; I can't say for sure without having a closer look.
What it almost certainly comes down to is with the different declared type: use of Object lacks enough information to know that value is of referential type, during serialization construction.
Whether it can be made to work or not is a different question.

Reopening assuming there is something to fix here. Thank you for the report!

[cowtowncoder]

Ok, this is working as designed: declared type MUST give indication that the value would be reference type (like Optional), and as such property declared as Object will not be filtered if it happens to contain a referential type.

In future we hope to support custom inclusion criteria which would allow construction of more advanced inclusion filters: for now, declared type has to be such that it allows determination of concept of absent.

I will keep this issue open, however, to think whether there is a possibility that this could be improved upon in future.

Also: I noticed that use of @JsonSerialize(as=Optional.class) does not work as expected; will file a separate bug.

[cowtowncoder]

Ok: so, fix here is two-fold. First, declared type MUST indicate it's a reference type (Optional), so declaration has to be something like:

public class JsonResult {
  @JsonSerialize(as=Optional.class) // important!
  private Object a;
  private Optional<Object> b;
}

The other part of the fix is to make sure Jackson actually uses type modified by annotation; this was not done but fix will be in 2.8.1. This combination will make tests pass.

One thing I do not understand, however, is why NON_EMPTY would not work here; it should work without additional type information. But I could not reproduce that issue; test actually works for me if NON_EMPTY is used.