docs: def update(self, key, value=None, dir=False, ttl=None, refresh=False,
                 prev_value=None, prev_index=None, timeout=None):
          """Updates an existing key."""
          return self.adapter.set(key, value, dir=dir, ttl=ttl, refresh=refresh,
                                  prev_value=prev_value, prev_index=prev_index,
                                  prev_exist=True, timeout=timeout)