book = self
rel_info = book.related_info()
names = [(related_tag_name(tag), Tag.create_url('author', tag['slug']))
- for tag in rel_info['tags']['author']]
+ for tag in rel_info['tags'].get('author', ())]
if 'parents' in rel_info:
books = [(name, Book.create_url(slug))
for name, slug in rel_info['parents']]