docs: def get(cls, bucket, key, version_id=None):
          """Fetch a specific object.
  
          By default the latest object version is returned, if
          ``version_id`` is not set.
  
          :param bucket: The bucket (instance or id) to get the object from.
          :param key: Key of object.
          :param version_id: Specific version of an object.
          """
          filters = [
              cls.bucket_id == as_bucket_id(bucket),
              cls.key == key,
          ]
  
          if version_id:
              filters.append(cls.version_id == version_id)
          else:
              filters.append(cls.is_head.is_(True))
              filters.append(cls.file_id.isnot(None))
  
          return cls.query.filter(*filters).one_or_none()