Add test case and special handling for Kotlin's object type

[luqasn]

Correctly deserialises

object SomeObject

into always the same reference instead of instantiating new ones.

Open to any feedback, not really that familiar with the codebase yet.

[luqasn]

Unfortunately, master branch seems broken :(

[apatrida]

What does this do if the values to deserialize differ from the values of the object instance? Does it use the object instance as-is or modify its values?

[luqasn]

It always takes the 'global' object instance and ignores whatever was to be deserialized. I have never used mutable objects because I think that is just bad design, but maybe you are right and it should be supported? Not sure...

[NayanSrivastav]

any update on this?

[luqasn]

I have read #225 and I think @apatrida raises valid concerns. But as using objects together with data classes with a sealed parent as kind of an enum type is Kotlin idiomatic, I would really expect the jackson-module-kotlin to support this out of the box.

In this use case, the objects being serialized and deserialized do not have any properties anyways, so maybe one could use the custom deserializer only exactly in this case? And throw an exception otherwise? Because I would prefer the deserializer not silently breaking my contract with the runtime (object being a singleton).

Still not great, but maybe better than the current state?

[cowtowncoder]

Closing in favor of patch #244.