code: @SuppressWarnings("unchecked")
    public <C extends CDACallback<CDASpace>> C fetchSpace(C callback) {
      return (C) Callbacks.subscribeAsync(observeSpace(), callback, this);
    }
docs: Asynchronously fetch the space.
  
  @param <C>      the type of the callback to be used.
  @param callback the value of the callback to be called back.
  @return the space for this client (asynchronously).