Empty options serialize to null since 2.7.4

[ieure]

I tried to upgrade Jackson in my Scala project today, and was met with several failing tests. I tracked this down to a behavior change from jackson-module-scala 2.7.3 -> 2.7.4. The issue is that empty Options now serialize to null. Prior to 2.7.3, they would be omitted from the output JSON.

Here's a project with a minimal failing testcase: https://github.com/ieure/jackson-scala-testcase

Based on this being an change in Option behavior & starting with 2.7.4, I suspect #252 is related to the breakage.

[ieure]

To clarify, this is still broken in 2.8.2.

[nbauernfeind]

Thanks for the clarification; that was going to be my first question! I have limited time, but will see what I can do tonight.

[cowtowncoder]

By default, empty Options SHOULD serialize to null unless there is specific configuration to do otherwise, as far as I know. This because default inclusion policy is JsonInclude.Include.ALWAYS.
To configure things globally, you can use any other JsonInclude.Include value except for ALWAYS or NON_NULL: so NON_EMPTY, NON_EMPTY or NON_DEFAULT should all exclude absent Option value.

To set default inclusion strategy you would use:

mapper.setSerializationInclusion(Include.NON_ABSENT)

or use @JsonInclude annotation on property in question.

Now: I don't think that a chance in patch version was intentional or the right way to do this; such fixes should be done in new minor versions. But going forward it sounds like the new behavior is the way things are supposed to work from Jackson perspective.

[ieure]

Hmm, NON_ABSENT seems to produce the behavior I expect, but I still find it surprising to get null in the output when I've selected Include.NON_NULL.

[cowtowncoder]

@ieure null here would mean that the property itself would be null, regardless of contents.
So NON_NULL definition is explicit JVM level null of value, even for referential types (Option, AtomicReference, guava/Java8 optionals).
I agree that things get bit hairy, but as of 2.7(.4) and beyond this should be the uniform definition. And also reason why additional values were added, to allow fine-grained levels.

For 2.9 I hope to finally add ability to define custom handlers because possible rules users want are unlimited: simplest ones can be enumerated, but there needs to be an extension point to allow even more elaborate checking.

FWIW, NON_ABSENT also includes what NON_NULL does, so it's a superset of things to exclude.

Hope this helps.

[jsw]

I also thought this was a bug. Would be great if this new behavior were documented. :-)

[cowtowncoder]

@jsw It is documented in Javadocs for @JsonInclude, but would be great if we got better wiki for in-depth explanation. Behavior is not really new for databind in general, but I think Scala module differed from it, so I guess it is new for Scala module.