docs: def get(cls, bucket, key, upload_id, with_completed=False):
          """Fetch a specific multipart object."""
          q = cls.query.filter_by(
              upload_id=upload_id,
              bucket_id=as_bucket_id(bucket),
              key=key,
          )
          if not with_completed:
              q = q.filter(cls.completed.is_(False))
  
          return q.one_or_none()