code: @SuppressWarnings("unchecked")
    public <C extends CDACallback<T>> C one(String id, C callback) {
      return (C) Callbacks.subscribeAsync(baseQuery().one(id), callback, client);
    }
docs: Async fetch resource matching the given {@code id}.
  
  @param id       resource id.
  @param callback callback.
  @param <C>      callback type.
  @return the given {@code callback} instance.