public TopicCreationGroup defaultTopicGroup() {
        return defaultTopicGroup;
    }
Return the default topic creation group. This group is always defined when topic creation is
enabled but is {@code null} if topic creation is disabled.

@return the default topic creation group if topic creation is enabled; {@code null} otherwise
connect/runtime/src/main/java/org/apache/kafka/connect/util/TopicCreation.java