1, create a subclass:
UnknownTokenException extends BatchRuntimeException
so users can configure it as skippable-exception to ignore certain content.

2, leverage various ignore mechanisms in jackson and expose them as configuration properties:
https://github.com/FasterXML/jackson-docs/wiki/JacksonHowToIgnoreUnknown
Some of them should already work w/ current jberet-support, just need to test it.