code: public SnsMessage.Builder<?> unmarshallBase(SnsMessage.Builder<?> builder, SnsJsonNode message) {
          return builder
              .withMessageId(message.getString(MESSAGE_ID))
              .withTopicArn(message.getString(TOPIC_ARN))
              .withTimestamp(message.getIso8601Date(TIMESTAMP));
      }
docs: Unmarshall the base properties of {@link SnsMessage}.
  
  @param builder Builder subclass to add base properties to.
  @param message JSON message.
  @return Modified builder with base properties added.