TypeError thrown in DefaultFormRendered::renderBegin()

[tvape]

Version: 3.2.8
PHP: 8.4.15

Bug Description

When you set a formally valid URL e.g. https://www.example.com/?foo as a form action and 'get' as the form method, the null value passed to urldecode() function throws TypeError in DefaultFormRenderer::renderBegin() method because $parts[1] is not set and the script has declare(strict_types=1); set:

TypeError: urldecode(): Argument #1 ($string) must be of type string, null given

public function renderBegin(): string
{
	$this->counter = 0;

	foreach ($this->form->getControls() as $control) {
		$control->setOption('rendered', false);
	}

	if ($this->form->isMethod('get')) {
		$el = clone $this->form->getElementPrototype();
		$el->action = (string) $el->action;
		$query = parse_url($el->action, PHP_URL_QUERY) ?: '';
		$el->action = str_replace("?$query", '', $el->action);
		$s = '';
		foreach (preg_split('#[;&]#', $query, -1, PREG_SPLIT_NO_EMPTY) as $param) {
			$parts = explode('=', $param, 2);
			$name = urldecode($parts[0]);
			$prefix = explode('[', $name, 2)[0];
			if (!isset($this->form[$prefix])) {
				$s .= Html::el('input', ['type' => 'hidden', 'name' => $name, 'value' => urldecode($parts[1])]);
			}
		}

		return $el->startTag() . ($s ? "\n\t" . $this->getWrapper('hidden container')->setHtml($s) : '');

	} else {
		return $this->form->getElementPrototype()->startTag();
	}
}

Steps To Reproduce

$form = new \Nette\Forms\Form();
$form->setAction('https://www.example.com/?foo');
$form->setMethod('get');
echo $form;

Expected Behavior

No exception thrown and parameter 'foo' set as a hidden input with an empty value.

Possible Solution

Solution is simply using null coalescing operator for urldecode($parts[1] ?? '')

$s .= Html::el('input', ['type' => 'hidden', 'name' => $name, 'value' => urldecode($parts[1] ?? '')]);