public void setConnectionSubjectFactory(ConnectionSubjectFactory connectionSubjectFactory) {
        if (connectionSubjectFactory == null) {
            throw new IllegalArgumentException("ConnectionSubjectFactory argument cannot be null.");
        }
        this.connectionSubjectFactory = connectionSubjectFactory;
    }
@Test(expected = IllegalArgumentException.class)
    public void setNullSubjectConnectionFactory() {
        filter.setConnectionSubjectFactory(null);
    }