public static void setExceptionObserver(LuceneExceptionObserver observer) {
    if (observer == null) {
      observer = exception -> {
      };
    }

    exceptionObserver = observer;
  }
An Async event queue listener that writes all of the events in batches to Lucene
geode-lucene/src/main/java/org/apache/geode/cache/lucene/internal/LuceneEventListener.java