"'NoneType' object has no attribute 'split'" on /browse/snapshot/log/

1. go to https://archive.softwareheritage.org/browse/snapshot/669100e5754a91c1e9b61626bb8e2de2a5bbee05/directory/
2. click "History" (or go to https://archive.softwareheritage.org/browse/snapshot/669100e5754a91c1e9b61626bb8e2de2a5bbee05/log/ directly)
3. you get this error: AttributeError: 'NoneType' object has no attribute 'split'

Sentry issue: SWH-WEBAPP-3H7

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Migrated from T3840 (view on Phabricator)