This issue affects token-sdk but also any cordapp developer, additionally it throws serialization exception masking real issue, which requires from our users to debug corda internals (there is a ticket for that as well).
OK, back to what's happening.
Let's define flow that has default parameter in the constructor (notice `JvmOverloads` annotation).
it throws <drums!>:
Anyway, this beauty comes from `net/corda/node/services/statemachine/FlowLogicRefFactoryImpl.kt:71`:
So, the default param is not visible...