Call to undefined method Illuminate\Validation\Rules\In::__set_state()

Question

i tried every method to resolve this, like clear cache,composer update/install, but after php artisan config:cache, it appears again.

In config.php line 839:
Call to undefined method Illuminate\Validation\Rules\In::__set_state()

and whole page turns to blank page. In bootstrap/cache/config.php file it shows:

'environment' => 
    array (
      'form' => 
      array (
        'rules' => 
        array (
          'app_name' => 'required|string|max:50',
          'environment' => 'required|string|max:50',
          'environment_custom' => 'required_if:environment,other|max:50',
          'app_debug' => 
          array (
            0 => 'required',
            1 => 
            Illuminate\Validation\Rules\In::__set_state(array(
               'rule' => 'in',
               'values' => 
              array (
                0 => 'true',
                1 => 'false',
              ),
            )),
          ),

Answer 1

I also got this error because instead of

"Illuminate\Validation\Rule"

I have put

"Illuminate\Contracts\Validation\Rule"