private void ensureSubscriberIsNull(String attemptingSubscribeMode) {
    if (subscriber != null) {
      throw new IllegalStateException(
          String.format(
              "Cannot use %s for consumption because a %s is already set for consumption.",
              attemptingSubscribeMode, subscriber.getClass().getSimpleName()));
    }
  }
Build the {@link LogKafkaSource}.

@return a LogKafkaSource with the settings made for this builder.
amoro-format-mixed/amoro-mixed-flink/amoro-mixed-flink-common/src/main/java/org/apache/amoro/flink/read/source/log/kafka/LogKafkaSourceBuilder.java