docs: def add_hashed_value(self, hash_value, store_key):
          """Add hashed value to the index.
  
          :param hash_value: The hashed value to be added to the index
          :type hash_value: str
          :param store_key: The key for the document in the store
          :type store_key: object
  
          """
          if self._unique and hash_value in self._index:
              raise NonUnique('Hash value {} already in index'.format(hash_value))
          if store_key not in self._index[hash_value]:
              self._index[hash_value].append(store_key)
          if hash_value not in self._reverse_index[store_key]:
              self._reverse_index[store_key].append(hash_value)