fun <T, U> FutureGet.onGetAllCustom(emitter: (data: U?, future: BaseFuture) -> Unit, transformer: (List<T>) -> U): Unit
A response has been received (for multiple elements) and you need to transform them, before returning.
emitter - callable, when the response has been received and transformed
transformer - callable, to transform the DHT's response type to the method's return type.
Note: when the response is null, the transformer is skipped, and returns null