public static OmemoService<?, ?, ?, ?, ?, ?, ?, ?, ?> getInstance() {
        if (INSTANCE == null) {
            throw new IllegalStateException("No OmemoService registered");
        }
        return INSTANCE;
    }
@Test(expected = IllegalStateException.class)
    public void getInstanceFailsWhenNullTest() {
        OmemoService.getInstance();
    }