flip() of ImmutableRoaringBitmap skips last bit of bitmap

[sirpkt]

flip() of ImmutableRoaringBitmap does not work correctly.
I skips the last bit of bitmap.
For example, with following test codes, the second test fails as ImmutableRoaringBitmap.flip() results in {1, 2} not {1}.
Both RoaringBitmap.flip() and MutableRoaringBitmap.flip() work fine.

  @Test
  public void fliptest1() {
    final MutableRoaringBitmap rb = new MutableRoaringBitmap();
    rb.add(0);
    rb.add(2);
    final MutableRoaringBitmap rb2 = MutableRoaringBitmap.flip(rb, 0, 3);
    final MutableRoaringBitmap result = new MutableRoaringBitmap();
    result.add(1);

    Assert.assertEquals(result, rb2);
  }

  @Test
  public void fliptest2() {
    final MutableRoaringBitmap rb = new MutableRoaringBitmap();
    rb.add(0);
    rb.add(2);
    final MutableRoaringBitmap rb2 = ImmutableRoaringBitmap.flip(rb, 0, 3);
    final MutableRoaringBitmap result = new MutableRoaringBitmap();
    result.add(1);

    Assert.assertEquals(result, rb2);
  }