Config.php, force_language issue

In the config.sample.php file of version 24 I read:

 * With this setting a language can be forced for all users. If a language is
 * forced, the users are also unable to change their language in the personal
 * settings. If users shall be unable to change their language, but users have
 * different languages, this value can be set to ``true`` instead of a language
 * code.
 * Defaults to ``false``
'force_language' => 'en',

This documentation is wrong, because nextcloud shows error, if I set to true:

OC\\L10N\\Factory::getUserLanguage(): Return value must be of type string, bool returned in file '/var/www/nextcloud/lib/private/L10N/Factory.php' line 426

I tested it in config/config.php
'force_language' => 'de',

Works for me. But i do not set something like false oder true.
Maybe the documentation is wrong not the software.

I thing Defaults belong to the fact it is not used.
And the parameter is only for the language if used.

If you add 'force_language' => true, to the config.php, it definitly causes the error @mareb is describing. On my test instance it also causes an internal server error, when I go to “Settings → Users”.

I think the description in the example file is just bad or incomplete, because this setting doesn’t make much sense on its own and the value “true” should probably only be used in combination with other language settings. Or how else would Nextcloud know which language it should “force”, respectively what would be the default language…?