fix: tweaks to datacite conversion

Author: sgfost

codemeticulous/datacite/convert.py

@@ -352,7 +352,8 @@ def canonical_to_datacite(
             codemeta_actors_to_datacite(data.publisher, Publisher)
         ),
         publicationYear=str(data.datePublished.year) if data.datePublished else None,
-        subjects=[Subject(subject=subject) for subject in ensure_list(data.keywords)],
+        subjects=[Subject(subject=subject) for subject in ensure_list(data.keywords)]
+        or None,
         contributors=codemeta_actors_to_datacite(data.contributor, Contributor),
         dates=[
             DateModel(
@@ -374,7 +375,7 @@ def canonical_to_datacite(
         formats=codemeta_language_fileformat_to_datacite_format(
             data.programmingLanguage, data.fileFormat
         ),
-        version=str(data.version),
+        version=str(data.version) if data.version else None,
         rightsList=codemeta_license_to_datacite_rights(data.license),
         descriptions=descriptions,
         # codemeta.funding is a plain string, can't really ensure that the string