fix trim null arg deprecation

[apreiml]

Avoid passing null as $string arg, because it causes a deprecation warning in php 8.6.4.

[realodix]

Avoid passing null as $string arg, because it causes a deprecation warning in php 8.6.4.

PHP 8.4.6 ?

[GrahamCampbell]

This change doesn't do anything because driver is never null by that point due to the very first line of the function.

[GrahamCampbell]

Ah, though getDefaultDriver has a bug where it can return null. code that calls parseDriver and getDefaultDriver assumes the result is non-null, even though the phpdoc return type says otherwise.