Fix Document entries with tags=None causing TypeError (v0.7.1) (#14)
The beancount printer iterates over entry.tags with sorted(entry.tags), which fails when tags is None. Changed Document creation to use frozenset() instead of None for both tags and links parameters. This fixes the error: TypeError: 'NoneType' object is not iterable Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>