/**
     * Special case to deal with Fatal errors and the like.
     */
    public function handleShutdown()
    {
        // If we reached this step, we are in shutdown handler.
        // An exception thrown in a shutdown handler will not be propagated
        // to the exception handler. Pass that information along.
        $this->canThrowExceptions = false;

        $error = $this->system->getLastError();
        if ($error && Misc::isLevelFatal($error['type'])) {
            // If there was a fatal error,
            // it was not handled in handleError yet.
            $this->allowQuit = false;
            $this->handleError(
                $error['type'],
                $error['message'],
                $error['file'],
                $error['line']
            );
        }
    }

    /**
     * In certain scenarios, like in shutdown handler, we can not throw exceptions
     * @var bool
     */
    private $canThrowExceptions = true;

    private function resolveHandler($handler)
    {
        if (is_callable($handler)) {
            $handler = new CallbackHandler($handler);
        }

        if (!$handler instanceof HandlerInterface) {
            throw new InvalidArgumentException(
                  "Handler must be a callable, or instance of "
                . "Whoops\\Handler\\HandlerInterface"