public function __construct($persistentValue = NULL)
{
parent::__construct();
$this->control->type = 'hidden';
$this->setOption('type', 'hidden');
if ($persistentValue !== NULL) {
$this->unmonitor(Nette\Forms\Form::class);
$this->persistValue = TRUE;
$this->value = (string) $persistentValue;
}
}