StateEventPayload
class StateEventPayload @InternalWowApi constructor(val name: String, val revision: Int, val payload: JsonNode)
One event of a StateEventRecord: its type name (context.aggregate.Event) and the payload as a JSON tree, both of the current revision of its schema: a stored event of an older revision is upgraded before it is published, and one stored under a former name is published under the current one.
Fields may be added: construct one with of; the constructor is internal to Wow.