If a function's response has a PersistedValueMutation type that is UNRECOGNIZED, we currently just silently ignore that mutation:
This is incorrect. The UNRECOGNIZED enum constant is a pre-defined constant used by the Protobuf Java SDK, to represent a constant that was unable to be deserialized (because the the serialized constant does not match any enums defined in the protobuf message).
Therefore, it should be handled by throwing an exception, preferably indicating that there is some sort of version mismatch between the function's Protobuf message definitions, and StateFun's Protobuf message definitions (i.e. most likely a mismatch in the invocation protocol versions).