Im getting the following error: Parse error: syntax error, unexpected '?', expecting variable (T_VARIABLE)

[Jatapiaro]

Symfony version(s) affected: Latest

Description
On production with PHP Version => 7.2.2-3+ubuntu16.04.1+deb.sury.org+1 I got the following error:
Parse error: syntax error, unexpected '?', expecting variable (T_VARIABLE)

How to reproduce
Just try to access any route on laravel. You need to include doctrine/dbal.

Possible Solution
The error throws the line 79 of the code.

 /**
     * @throws InvalidArgumentException If a locale contains invalid characters
     */
    public function __construct(?string $locale, MessageFormatterInterface $formatter = null, string $cacheDir = null, bool $debug = false)
    {
        $this->setLocale($locale);
 
        if (null === $formatter) {
            $formatter = new MessageFormatter();
        }
 
        $this->formatter = $formatter;
        $this->cacheDir = $cacheDir;
        $this->debug = $debug;
    }

That line corresponds to the method declaration, why does it have a ?string, I just removed that ? and everything works fine.

Also I have this stackoverflow issue if you need more information: https://stackoverflow.com/questions/51698746/how-to-fix-a-syntax-error-on-symfony-component-raised-after-composer-require-doc?noredirect=1#comment90359711_51698746

[kaznovac]

check your php version

[xabbuh]

This error message happens when your PHP version is below PHP 7.1 which introduced nullable type hints (see http://php.net/manual/en/migration71.new-features.php). When checking the PHP version, keep in mind that the version used on CLI can be different from the one used by the web server.