@ParametricNullness C closeable, Executor closingExecutor) {
      checkNotNull(closingExecutor);
      if (closeable != null) {
        list.add(closeable, closingExecutor);
      }
      return closeable;
    }
  }

  /**
   * An operation that computes a result.
   *
   * @param <V> the type of the result
   */

   * but it is observed to be true for OpenJDK 1.7. It also can't be guaranteed that the method
   * isn't inadvertently <i>oversizing</i> the returned map.
   *
   * @param expectedSize the number of entries you expect to add to the returned map
   * @return a new, empty {@code HashMap} with enough capacity to hold {@code expectedSize} entries
   *     without resizing
   * @throws IllegalArgumentException if {@code expectedSize} is negative
   */