// has now been moved after index.
        return new MoveDesc<>(actualLastElement, changes.replaced);
      }
    }
    // Trickled element was after index to begin with, no adjustment needed.
    return changes;
  }

  @CheckForNull
  private MoveDesc<E> fillHole(int index, E toTrickle) {
    Heap heap = heapForIndex(index);