Fix null to empty mapping for enum sets

[DavidRigglemanININ]

The ideal fix here would probably be in jackson core and specifically that NullsAsEmptyProvider works with EnumSet, but it currently does not, so this is a workaround that solves the problem for now.

[cowtowncoder]

@DavidRigglemanININ reporting it as a bug would help: I noticed this and created:

FasterXML/jackson-databind#2529

and null handling for EnumSet will now be improved to same level as regular Collections and Maps in 2.1.0.1

[DavidRigglemanININ]

Great! Feel free then to close this PR. It seems like activity has picked up this module, but for a while, there was little activity and workarounds were necessary if the fix wasn't going to be made immediately, and I wanted to at least make my changes visible to others in case they were useful.

[apatrida]

all good @DavidRigglemanININ, I think we should add a test case to show this, and make sure it is fixed in 2.10.1 from the perspective of this report.

[DavidRigglemanININ]

all good @DavidRigglemanININ, I think we should add a test case to show this, and make sure it is fixed in 2.10.1 from the perspective of this report.

This PR has a test case for null to empty enum set, so feel free to use that if you want.

[cowtowncoder]

@DavidRigglemanININ thank you for offering the patch -- totally understandable wrt workarounds.

[DavidRigglemanININ]

Assuming this is shown to work in 2.10.1 without my patch, we can close out this PR if you want.

[cowtowncoder]

I think problem has been fixed, but if I was mistaken, please re-file issue for Kotlin module and it can be re-investigated.

[DavidRigglemanININ]

I confirmed the problem is fixed in 2.10.1 of the jackson-module-kotlin without my fix.

[cowtowncoder]

@DavidRigglemanININ thank you for verification.