public Set<InternalTopicConfig> nonSourceChangelogTopics() {
            final Set<InternalTopicConfig> topicConfigs = new HashSet<>();
            for (final Map.Entry<String, InternalTopicConfig> changelogTopicEntry : stateChangelogTopics.entrySet()) {
                if (!sourceTopics.contains(changelogTopicEntry.getKey())) {
                    topicConfigs.add(changelogTopicEntry.getValue());
                }
            }
            return topicConfigs;
        }
Returns the config for any changelogs that must be prepared for this topic group, ie excluding any source
topics that are reused as a changelog
streams/src/main/java/org/apache/kafka/streams/processor/internals/InternalTopologyBuilder.java