should add try... catch... statement

[pigLoveRabbit]

 $slimResponse = $this->app->process($slimRequest, new Http\Response());

Slim

 try {
    ob_start();
    $response = $this->process($this->container->get('request'), $response);
} catch (InvalidMethodException $e) {
    $response = $this->processInvalidMethod($e->getRequest(), $response);
} finally {
    $output = ob_get_clean();
}

According to the source code of Slim, here may throw a exception(InvalidMethodException)

[Mariano Benítez Mulet]

Yes, indeed, you might see not only InvalidMethodException but a NotFoundException as well.
The example is does not contain it in order not to influence or suggest how to handle exceptions, which depends purely on your requirements.