'redis' as php_save_handler

[ozcelebi]

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Just upgrade from 2.8.0 to 2.8.1 and noticed that the save_handler is treated differently now

Code to reproduce the issue

You can reproduce it by using a redis server as your session handler.
Here is part of our code, obviously I can't share the full thing.

$config['session'] = [
    'php_save_handler' => 'redis',
    'save_path' => 'XXX',
    'gc_maxlifetime' => 60 * 60 * 24
];

Actual results

Zend\Session\Exception\InvalidArgumentException: Invalid save handler specified ("redis"); must be one of "files" or a class implementing SessionHandlerInterface

Expected

Either there needs to be a Redis SaveHandler class or it should be treated just like 'files'

Sidenote

The example in the Documentation now breaks,
https://framework.zend.com/manual/2.4/en/modules/zend.session.config.html#id3