TopicFilter topicFilter() {
        return getConfiguredInstance(TOPIC_FILTER_CLASS, TopicFilter.class);
    }
@Test
    public void testNoTopics() {
        MirrorSourceConfig config = new MirrorSourceConfig(makeProps("topics", ""));
        assertFalse(config.topicFilter().shouldReplicateTopic("topic1"), "topic1 shouldn't exist");
        assertFalse(config.topicFilter().shouldReplicateTopic("topic2"), "topic2 shouldn't exist");
        assertFalse(config.topicFilter().shouldReplicateTopic(""), "Empty topic shouldn't exist");
    }