@Override
    public boolean isEmpty() {
        if (rangeBitSetMap.isEmpty()) {
            return true;
        }
        for (BitSet rangeBitSet : rangeBitSetMap.values()) {
            if (!rangeBitSet.isEmpty()) {
                return false;
            }
        }
        return true;
    }
@Test
    public void testIsEmpty() {
        OpenLongPairRangeSet<LongPair> set = new OpenLongPairRangeSet<>(consumer);
        assertTrue(set.isEmpty());
        // lowerValueOpen and upperValue are both -1 so that an empty set will be added
        set.addOpenClosed(0, -1, 0, -1);
        assertTrue(set.isEmpty());
        set.addOpenClosed(1, 1, 1, 5);
        assertFalse(set.isEmpty());
    }