The original php method preg_split might return `string[][]` in some
situations, however this should never be the case for this library. By
adding an extra assert, we should be more safe.
Correctly flagged by Psalm:
```
ERROR: PossiblyNullArgument - src\Utils.php:50:53 - Argument 3 of preg_split cannot be null, possibly null value provided (see https://psalm.dev/078)
$parts = php_preg_split($pattern, $subject, $limit, $flags);
```
The `$limit` argument of the PHP native `preg_split()` function is not nullable.
Ref: https://www.php.net/manual/en/function.preg-split
Jaapio
jrfnl