cfg apply results in Aws::CloudFront::Errors::MalformedInput

[yanokwa]

We run s3_website cfg apply on every merge to master to make sure new redirects get published. When we do that now, we get the Aws::CloudFront::Errors::MalformedInput error.

$ s3_website cfg apply

Applying the configurations in s3_website.yml on the AWS services ...
Bucket opendatakit.org now functions as a website
38 redirects configured for opendatakit.org bucket
Bucket example.org is now readable to the whole world
Detected an existing CloudFront distribution (id E1EZ24MS8LWP3O) ...
Unexpected list element termination (Aws::CloudFront::Errors::MalformedInput)
Exited with code 1

Source file: https://github.com/opendatakit/website/blob/master/s3_website.yml

Removal of the following block causes the problem to go away.

cloudfront_distribution_config:
  default_cache_behavior:
    min_ttl: <%= 60 * 60 * 24 %>
  aliases:
    quantity: 2
    items:
      - opendatakit.org
      - www.opendatakit.org

s3_website.yml shows up as valid YML and there hasn't been any change in our infrastructure that would explain this error. Is there anyway to get more debug information?