docs: public UserManagedCacheBuilder<K, V, T> withKeyCopier(Copier<K> keyCopier) {
      if (keyCopier == null) {
        throw new NullPointerException("Null key copier");
      }
      UserManagedCacheBuilder<K, V, T> otherBuilder = new UserManagedCacheBuilder<>(this);
      otherBuilder.keyCopier = keyCopier;
      otherBuilder.useKeySerializingCopier = false;
      return otherBuilder;
    }