Fatal error: Uncaught UnexpectedValueException: PHP Startup: Failed to open directory: No such file or directory

[ben221199]

With the following code...

#!/usr/bin/env php
<?php
use Composer\Autoload\ClassLoader;
use Practically\Preloading\Preloader;

/** @var ClassLoader*/
$autoloader = require __DIR__ . '/vendor/autoload.php';
$preloader = new Preloader($autoloader);

$preloader->preload('/^app/');

$preloader->preloadDirectory(__DIR__.'/resources/views');
$preloader->preloadDirectory(__DIR__.'/views');

var_dump(opcache_get_status(true));

...I get the following error:

Fatal error:  Uncaught UnexpectedValueException: PHP Startup: Failed to open directory: No such file or directory in /var/www/html/vendor/practically/preloader/src/Preloader.php:56
	Stack trace:
		#0 /var/www/html/vendor/practically/preloader/src/Preloader.php(56): RecursiveDirectoryIterator->__construct('/var/www/html/v...')
		#1 /var/www/html/preload.php(13): Practically\Preloading\Preloader->preloadDirectory('/var/www/html/v...')
	thrown in /var/www/html/vendor/practically/preloader/src/Preloader.php on line 56