`Configuration.dump` raises `StopIteration` if the last line is empty.

`yaml_util.restore_yaml_comments` has an explicit call to `next` without catching `StopIteration`, which is raised if the last processed line is empty or a comment. This seems to happen in `Configuration.dump` if the last line of `config_default.yaml` is empty or a comment.

Start in yaml_util.restore_yaml_comments and trace how Configuration.dump processes config_default.yaml. Reproduce the failure with a final empty or comment line, then verify that dumping such a configuration completes without StopIteration.

Written by the indexing model from the issue text.