Error: Call to a member function?

Fatal error: Uncaught Error: Call to a member function send() on string in /var/www/app/App.php:95 Stack trace: #0 /var/www/public/index.php(10): App\App->run() #1 {main} thrown in /var/www/app/App.php on line 95

public function run()
    {
        $matcher = new UrlMatcher($this->routes, $this->requestContext);
        try {
            $this->request->attributes->add($matcher->match($this->request->getPathInfo()));
            $this->controller = $this->getController();
            $this->arguments = $this->getArguments($this->controller);

            $response = call_user_func($this->controller, $this->arguments);
        } catch (ResourceNotFoundException $e) {
            echo $e->getMessage();
        }


        if (!empty($response)) {
            $response->send();
        }