code: public function __unsetHook()
      {
          return function ($next, $value, $args) {
              $key = $args->get('key');
  
              if ($this->hasMeta($key)) {
                  return $this->setMeta($key, null);
              }
  
              return $next($value, $args);
          };
      }
docs: Register hook on unset call.
  
  @return \Closure