docs: protected Serializer serializer() {
      Serializer serializer = this.serializer;
      if (serializer == null) {
        synchronized (this) {
          serializer = this.serializer;
          if (serializer == null) {
            NamespaceConfig config = this.config.getNamespaceConfig();
            if (config == null) {
              serializer = Serializer.using(Namespaces.BASIC);
            } else {
              serializer = Serializer.using(Namespace.builder()
                  .register(Namespaces.BASIC)
                  .nextId(Namespaces.BEGIN_USER_CUSTOM_ID)
                  .register(new Namespace(config))
                  .build());
            }
            this.serializer = serializer;
          }
        }
      }
      return serializer;
    }