The comment in the code describes the issue
```

1. No release tag exists locally for this FCV. This happens when a new latest FCV
2. is introduced before its first tag is visible to this clone. For example, when
3. LATEST_FCV became 9.1, tasks running on that revision saw no r9.1.* tag until
4. r9.1.0-alpha0 had propagated. Skip such an FCV rather than yielding None, which
5. would fail deep inside a subprocess call.
   ```

Fixes https://jira.mongodb.org/browse/BF-45571