Form with POST return null

https://codeigniter4.github.io/CodeIgnit...aceholders

! Note:
{locale} cannot be used as a placeholder or other part of the route, as it is reserved for use in localization.

I have used it in every route of my web  and it works, I also tried to write the ulr without {locale}, and still dosen't work

In Routes
The second method uses a custom placeholder to detect the desired locale and set it on the Request. The placeholder 

Code:

{locale}

 can be placed as a segment in your route. If present, the contents of the matching segment will be your locale:

PHP Code:

$routes->get('{locale}/books','App\Books::index');