* which are <i>not the caller's fault</i>. Doing so is <b>not recommended</b> because it is
 * misleading to future readers of the code and of stack traces. See <a
 * href="https://github.com/google/guava/wiki/ConditionalFailuresExplained">Conditional failures
 * explained</a> in the Guava User Guide for more advice. Notably, {@link Verify} offers assertions

  @ParametricNullness
  private V getDoneValue(Object obj) throws ExecutionException {
    // While this seems like it might be too branch-y, simple benchmarking proves it to be
    // unmeasurable (comparing done AbstractFutures with immediateFuture)
    if (obj instanceof Cancellation) {
      throw cancellationExceptionWithCause("Task was cancelled.", ((Cancellation) obj).cause);

 * which are <i>not the caller's fault</i>. Doing so is <b>not recommended</b> because it is
 * misleading to future readers of the code and of stack traces. See <a
 * href="https://github.com/google/guava/wiki/ConditionalFailuresExplained">Conditional failures
 * explained</a> in the Guava User Guide for more advice. Notably, {@link Verify} offers assertions

   * listeners for future n may complete before some for future n-1.) However, it is possible, if
   * one input completes with result X and another later with result Y, for Y to come before X in
   * the output future list. (Such races are impossible to solve without global synchronization of
   * all future completions. And they should have little practical impact.)
   *