protected function validateMountPage(array $mountPage)
    {
        $isValidMountPage = true;

        if (empty($mountPage['mountPageSource'])) {
            $isValidMountPage = false;

            $flashMessage = GeneralUtility::makeInstance(
                FlashMessage::class,
                'Property "Mounted page" must not be empty. Invalid Mount Page configuration for page ID ' . $mountPage['uid'] . '.',
                'Failed to initialize Mount Page tree. ',
                FlashMessage::ERROR
            );
            $this->flashMessageQueue->addMessage($flashMessage);
        }

        if (!$this->mountedPageExists($mountPage['mountPageSource'])) {
            $isValidMountPage = false;

            $flashMessage = GeneralUtility::makeInstance(
                FlashMessage::class,
                'The mounted page must be accessible in the frontend. '
                . 'Invalid Mount Page configuration for page ID '
                . $mountPage['uid'] . ', the mounted page with ID '
                . $mountPage['mountPageSource']
                . ' is not accessible in the frontend.',
                'Failed to initialize Mount Page tree. ',
                FlashMessage::ERROR
            );
            $this->flashMessageQueue->addMessage($flashMessage);
        }

        return $isValidMountPage;
    }