We used to add a JsonWrap unconditionally to the request body even if it is not a required parameter. This has caused several problems in the past, which we have fixed by explicitly setting the problematic values to, say, an empty map or array. This time, it causes conduwuit to reject our request to upload keys because it wrongfully sends a `null` value in `one_time_keys`, but it is expecting a map, or the kv should not appear in the body at all.
We now fix this for good by adding a null check for JsonWrap values in `addToJsonIfNeeded()`.
BUG: https://iron.lily-is.land/T133