public function fieldExists($field, TraversableElement $container = null)
    {
        $container = $container ?: $this->session->getPage();
        $node = $container->findField($field);

        if (null === $node) {
            throw new ElementNotFoundException($this->session->getDriver(), 'form field', 'id|name|label|value', $field);
        }

        return $node;
    }