@Override
    public boolean add(E element) {
        return add(element, element.hashCode());
    }
@Test(expected = NullPointerException.class)
    public void testContainsAllThrowsOnNullElement() {
        final OAHashSet<Integer> set = new OAHashSet<>(8);
        set.add(1);

        final Collection<Integer> elementsToCheck = new ArrayList<>(2);
        elementsToCheck.add(1);
        elementsToCheck.add(null);

        set.containsAll(elementsToCheck);
    }