pypi.loader: Filter out null snapshot branch

Related T1396

swh/loader/pypi/loader.py

@@ -113,7 +113,7 @@ class PyPILoader(SWHLoader):
         # retrieve only revisions (e.g the alias we do not want here)
         revs = [rev['target']
                 for rev in last_snapshot['branches'].values()
-                if rev['target_type'] == 'revision']
+                if rev and rev['target_type'] == 'revision']
         known_revisions = self.storage.revision_get(revs)
         ret = {}
         for revision in known_revisions:

[Phabricator Migration user]

Some references in the commit message have been migrated:

• T1396 is now swh-loader-core#1396 (closed)