Argument 3 passed to Symfony\Component\HttpKernel\Exception\ServiceUnavailableHttpException::__construct() must be an instance of Exception or null, array given

Problem/Motivation

The following error has been showing in error logs:

php-error ded-15106 [20-Jan-2021 22:56:13 UTC] TypeError: Argument 3 passed to Symfony\Component\HttpKernel\Exception\ServiceUnavailableHttpException::__construct() must be an instance of Exception or null, array given, called in REDACTED/fast_404/src/Fast404.php on line 214 in REDACTED/vendor/symfony/http-kernel/Exception/ServiceUnavailableHttpException.php on line 25 #0 REDACTED/fast_404/src/Fast404.php(214): Symfony\Component\HttpKernel\Exception\ServiceUnavailableHttpException->__construct(3, 'The requested U...', Array)

Proposed resolution

Use the $this->t function for the exception message:

throw new ServiceUnavailableHttpException(3, $this->t('The requested URL "@path" was not found on this server. Try again shortly.', ['@path' => $this->request->getPathInfo()]));