in src/main/java/software/amazon/sns/AmazonSNSExtendedClient.java [222:229]
private PublishRequest copyPublishRequest(PublishRequest publishRequest) {
// We only modify Message and MessageAttributes, to avoid performance impact let's shallow-copy
// the request and then copy the MessageAttributes map.
PublishRequest clonedPublishRequest = publishRequest.clone();
Map<String, MessageAttributeValue> attributes = new HashMap<>(publishRequest.getMessageAttributes());
clonedPublishRequest.setMessageAttributes(attributes);
return clonedPublishRequest;
}