code: def update(self, new_keys: Index):
          
          if not self._map.index.intersection(new_keys).empty:
              raise KeyError("Non-unique keys in index.")
  
          mapping_update = self.hash_(new_keys)
          if self._map.empty:
              self._map = mapping_update.drop_duplicates()
          else:
              self._map = self._map.append(mapping_update).drop_duplicates()
  
          collisions = mapping_update.index.difference(self._map.index)
          salt = 1
          while not collisions.empty:
              mapping_update = self.hash_(collisions, salt)
              self._map = self._map.append(mapping_update).drop_duplicates()
              collisions = mapping_update.index.difference(self._map.index)
              salt += 1
docs: Adds the new keys to the mapping.
  
          Parameters
          ----------
          new_keys :
              The new index to hash.