@Override
  protected CompletionStage<Collection<Void>> handleMessageAsync(M message, MessageCollector collector,
      TaskCoordinator coordinator) {
    this.sinkFn.apply(message, collector, coordinator);
    // there should be no further chained operators since this is a terminal operator.
    return CompletableFuture.completedFuture(Collections.emptyList());
  }
An operator that sends incoming messages to an arbitrary output system using the provided {@link SinkFunction}.
samza-core/src/main/java/org/apache/samza/operators/impl/SinkOperatorImpl.java