docs: def init(self, key_value_pairs):
          """Initialize datastore.
  
          Only sets values for keys that are not in the datastore already.
  
          :param dict key_value_pairs:
              A set of key value pairs to use to initialize the datastore.
          """
          for k, v in key_value_pairs.items():
              if k not in DatastoreLegacy.store[self.domain]:
                  DatastoreLegacy.store[self.domain][k] = v