code: public static MutableRoaringBitmap xor(ImmutableRoaringBitmap... bitmaps) {
      return groupByKey(bitmaps)
              .entrySet()
              .parallelStream()
              .collect(XOR);
    }
docs: Computes the bitwise symmetric difference of the input bitmaps
  @param bitmaps the input bitmaps
  @return the symmetric difference of the bitmaps