How to use the @gapi/core.GraphQLNonNull function in @gapi/core

withFilter(
      function(self: ClientController) {
        return self.pubsub.asyncIterator('listenForChanges');
      },
      function(global, unused, payload, context) {
        const isCorrectLength = context.clientid.length + context.clientid.length;
        if (isCorrectLength === 100 && payload.clientId === context.clientid) {
          return true;
        }
        return false;
      }
    )
  )
  @Subscription({
    clientId: {
      type: new GraphQLNonNull(GraphQLString)
    }
  })
  async listenForChanges(views: ConfigViews) {
    return this.getViewsConfig(views);
  }

  getViewsConfig(views?: ConfigViews) {
    const config = Container.get('main-config-compiled');
    return {
      components: config.$components,
      views: viewsToArray(views || config.$views),
      schema: printSchema(Container.get(BootstrapService).schema)
    };
  }

  @Type(ClientType)