@Override
    public boolean add(T newValue) {
        Objects.requireNonNull(newValue);
        return snapshottableAddUnlessPresent(new TimelineHashSetEntry<>(newValue));
    }
@Test
    public void testNullsForbidden() {
        SnapshotRegistry registry = new SnapshotRegistry(new LogContext());
        TimelineHashSet<String> set = new TimelineHashSet<>(registry, 1);
        assertThrows(NullPointerException.class, () -> set.add(null));
    }