*     {@link #whenAllComplete(Iterable)} or {@link #whenAllComplete(Iterable)}
     * @throws IllegalStateException if called outside of a call to {@link
     *     CombiningCallable#call(DeferredCloser, Peeker)} or {@link
     *     AsyncCombiningCallable#call(DeferredCloser, Peeker)}
     */
    @ParametricNullness
    public final <D extends @Nullable Object> D getDone(ClosingFuture<D> closingFuture)