This rule seems to be also valuable in PHP, see \http://php.vrana.cz/variable-initialization-in-php.php and \https://code.google.com/archive/p/php-initialized/
And I have the feeling that even in Java or C# for instance for which the default values of primitive types is known, this is a kind of reliability issue to rely on some paths on the those default values. (cc [~ann.campbell.2])