SageMaker-Seq2Seq-Translation-English-German.ipynb failed CI

Link to the notebook:
https://github.com/aws/amazon-sagemaker-examples/blob/master/introduction_to_amazon_algorithms/seq2seq_translation_en-de/SageMaker-Seq2Seq-Translation-English-German.ipynb

Error:

---------------------------------------------------------------------------
Exception encountered at "In [8]":
---------------------------------------------------------------------------
ParamValidationError Traceback (most recent call last)
in
5 s3.Bucket(bucket).put_object(Key=key, Body=data)
6
----> 7 upload_to_s3(bucket, prefix, 'train', 'train.rec')
8 upload_to_s3(bucket, prefix, 'validation', 'val.rec')
9 upload_to_s3(bucket, prefix, 'vocab', 'vocab.src.json')

in upload_to_s3(bucket, prefix, channel, file)
3 data = open(file, "rb")

[...]

Invalid bucket name "": Bucket name must match the regex "^[a-zA-Z0-9.\-_]{1,255}$" or be an ARN matching the regex "^arn:(aws).*:s3:[a-z\-0-9]+:[0-9]{12}:accesspoint[/:][a-zA-Z0-9\-]{1,63}$|^arn:(aws).*:s3-outposts:[a-z\-0-9]+:[0-9]{12}:outpost[/:][a-zA-Z0-9\-]{1,63}[/:]accesspoint[/:][a-zA-Z0-9\-]{1,63}$"