diff --git a/swh/indexer/metadata_dictionary/npm.py b/swh/indexer/metadata_dictionary/npm.py
--- a/swh/indexer/metadata_dictionary/npm.py
+++ b/swh/indexer/metadata_dictionary/npm.py
@@ -99,14 +99,18 @@
         {'@list': [{'@type': 'http://schema.org/Person',
                     'http://schema.org/email': 'john.doe@example.org',
                     'http://schema.org/name': 'John Doe',
-                    'http://schema.org/url': {'@id': 'https://example.org/~john.doe'}}]}
+                    'http://schema.org/url': {
+                        '@id': 'https://example.org/~john.doe'
+                    }}]}
         >>> pprint(NpmMapping().normalize_author(
         ...     'John Doe <john.doe@example.org> (https://example.org/~john.doe)'
         ... ))
         {'@list': [{'@type': 'http://schema.org/Person',
                     'http://schema.org/email': 'john.doe@example.org',
                     'http://schema.org/name': 'John Doe',
-                    'http://schema.org/url': {'@id': 'https://example.org/~john.doe'}}]}
+                    'http://schema.org/url': {
+                        '@id': 'https://example.org/~john.doe'
+                    }}]}
         """ # noqa
         author = {'@type': SCHEMA_URI+'Person'}
         if isinstance(d, dict):