Nette 2 kam zmizol FormContainer?

kam prosim Vas zmizol FormContainer? mam v bootstrape konkretne tento kod kde dojde k chybe:

<?php
//metoda addDatePicker do FormContaineru
Nette\Forms\FormContainer::extensionMethod('addDatePicker', function (FormContainer $container, $name, $label = NULL) {
    return $container[$name] = new DatePicker($label);
});
?>

ma to pridat moznost $form->addDatePicker, no hadze to chybu ze triedu FormContainer nemoze najst, prosim pomozte.