docs: def load_from_store(self):
          """Load index from store.
  
          :return: Whether index was correctly loaded or not
          :rtype: bool
          :raise AttributeError: If no datastore is defined
  
          """
          if not self._store:
              raise AttributeError('No datastore defined!')
          if self._store.has_blob('all_keys'):
              data = Serializer.deserialize(self._store.get_blob('all_keys'))
              self.load_from_data(data)
              return True
          elif self._store.has_blob('all_keys_with_undefined'):
              blob = self._store.get_blob('all_keys_with_undefined')
              data = Serializer.deserialize(blob)
              self.load_from_data(data, with_undefined=True)
              return True
          else:
              return False