docs: public UserManagedCacheBuilder<K, V, T> withKeySerializer(Serializer<K> keySerializer) {
      if (keySerializer == null) {
        throw new NullPointerException("Null key serializer");
      }
      UserManagedCacheBuilder<K, V, T> otherBuilder = new UserManagedCacheBuilder<>(this);
      otherBuilder.keySerializer = keySerializer;
      return otherBuilder;
    }