core-bundle/src/Resources/contao/dca/tl_page.php
public function makeRedirectPageMandatory(Contao\DataContainer $dc)
	{
		$objPage = $this->Database->prepare("SELECT * FROM " . $dc->table . " WHERE id=?")
								  ->limit(1)
								  ->execute($dc->id);

		if ($objPage->numRows && $objPage->type == 'logout')
		{
			$GLOBALS['TL_DCA']['tl_page']['fields']['jumpTo']['eval']['mandatory'] = true;
		}
	}
public function makeRedirectPageMandatory(Contao\DataContainer $dc)
	{
		$objPage = $this->Database->prepare("SELECT * FROM " . $dc->table . " WHERE id=?")
								  ->limit(1)
								  ->execute($dc->id);

		if ($objPage->numRows && $objPage->type == 'logout')
		{
			$GLOBALS['TL_DCA']['tl_page']['fields']['jumpTo']['eval']['mandatory'] = true;
		}
	}
Make the redirect page mandatory if the page is a logout page

@param Contao\DataContainer $dc

@throws Exception