code: public function __issetHook()
      {
          return function ($next, $isset, $args) {
              $key = $args->get('key');
  
              if (!$isset) {
                  $isset = (bool) $this->hasMeta($key);
              }
  
              return $next($isset, $args);
          };
      }
docs: Register hook on isset call.
  
  @return \Closure