@Override
  public void handleSourceEvents(SourceEvent sourceEvent) {
    if (!(sourceEvent instanceof InitializationFinishedEvent)) {
      return;
    }
    LOGGER.info("receive InitializationFinishedEvent");
    maxWatermarkToBeEmitted = true;
    emitWatermarkIfNeeded();
  }
SourceEvents may be received before this#pollNext.
amoro-format-mixed/amoro-mixed-flink/amoro-mixed-flink-common/src/main/java/org/apache/amoro/flink/read/hybrid/reader/MixedFormatSourceReader.java