if (collection.isEmpty()) {
        return false;
      }
      int oldSize = size(); // calls refreshIfEmpty
      boolean changed = delegate.addAll(collection);
      if (changed) {
        int newSize = delegate.size();
        totalSize += newSize - oldSize;
        if (oldSize == 0) {
          addToMap();
        }
      }
      return changed;
    }

    @Override

  private static int[] expandAndFillWithAbsent(int[] array, int newSize) {
    int oldSize = array.length;
    int[] result = Arrays.copyOf(array, newSize);
    Arrays.fill(result, oldSize, newSize, ABSENT);
    return result;
  }

  @Override
  public int size() {
    return size;
  }

  /**