public function existPermission($permissionName)
    {
        $permission = $this->permissions->first(function ($key, $value) use ($permissionName) {
            return ((isset($key->name)) ? $key->name : $value->name) == $permissionName;
        });

        if (! empty($permission)) {
            $active = (is_null($permission->pivot->expires) or $permission->pivot->expires->isFuture());

            if ($active) {
                return (bool) $permission->pivot->value;
            }
        }

        return false;
    }