private <T extends Throwable> T onAbort(UploadObjectObserver observer, T t) {
        observer.onAbort();
        return t;
    }
Convenient method to notifies the observer to abort the multi-part
upload, and returns the original exception.
aws-java-sdk-s3/src/main/java/com/amazonaws/services/s3/AmazonS3EncryptionClient.java