Allowing Serialize any class that extends a ScalaJsonSerializable trait. And add serializers for java AbstractCollection and Map, needed for wrapped scala collection.
Handling circular reference on case class serialization.
A object don't start his serialization for the second time until it completes the first serialization.

Eg:
  A references B and C,
  C references B,
  B refrences D,
  D references B,

The serialization path is:
   A -> B -> D
   |--> C -> B -> D

When it reach "D", it won't serialize the B instance anymore, cause B has a unfinished serialization in progress.

That behaviour may change. That way fix the StackOverflow problem, but don't allow deserializing properly.