Steps to reproduce the issue

When testing Joomla 4.0.4 with php 8.1 it gave the following errors in the frontend with the line

Call to a member function getTag() on null

in /home/test/public_html/libraries/src/WebAsset/AssetItem/LangActiveAssetItem.php (line 46)
$langTag = Factory::getApplication()->getLanguage()->getTag();

Error:
Call to a member function getTag() on null

at /home/test/public_html/libraries/src/WebAsset/AssetItem/LangActiveAssetItem.php:46
at Joomla\CMS\WebAsset\AssetItem\LangActiveAssetItem->__construct()
(/home/test/public_html/libraries/src/WebAsset/WebAssetRegistry.php:241)
at Joomla\CMS\WebAsset\WebAssetRegistry->createAsset()
(/home/test/public_html/libraries/src/WebAsset/WebAssetRegistry.php:424)
at Joomla\CMS\WebAsset\WebAssetRegistry->parseRegistryFile()
(/home/test/public_html/libraries/src/WebAsset/WebAssetRegistry.php:347)
at Joomla\CMS\WebAsset\WebAssetRegistry->parseRegistryFiles()
(/home/test/public_html/libraries/src/WebAsset/WebAssetRegistry.php:128)
at Joomla\CMS\WebAsset\WebAssetRegistry->get()
(/home/test/public_html/libraries/src/WebAsset/WebAssetManager.php:257)
at Joomla\CMS\WebAsset\WebAssetManager->useAsset()
(/home/test/public_html/libraries/src/WebAsset/WebAssetManager.php:225)
at Joomla\CMS\WebAsset\WebAssetManager->__call()
(/home/test/public_html/templates/cassiopeia/error.php:38)
at require('/home/test/public_html/templates/cassiopeia/error.php')
(/home/test/public_html/libraries/src/Document/HtmlDocument.php:771)
at Joomla\CMS\Document\HtmlDocument->_loadTemplate()
(/home/test/public_html/libraries/src/Document/HtmlDocument.php:830)
at Joomla\CMS\Document\HtmlDocument->_fetchTemplate()
(/home/test/public_html/libraries/src/Document/HtmlDocument.php:633)
at Joomla\CMS\Document\HtmlDocument->parse()
(/home/test/public_html/libraries/src/Document/HtmlDocument.php:652)
at Joomla\CMS\Document\HtmlDocument->render()
(/home/test/public_html/libraries/src/Document/ErrorDocument.php:140)
at Joomla\CMS\Document\ErrorDocument->render()
(/home/test/public_html/libraries/src/Error/Renderer/HtmlRenderer.php:77)
at Joomla\CMS\Error\Renderer\HtmlRenderer->render()
(/home/test/public_html/libraries/src/Exception/ExceptionHandler.php:128)
at Joomla\CMS\Exception\ExceptionHandler::render()
(/home/test/public_html/libraries/src/Exception/ExceptionHandler.php:71)
at Joomla\CMS\Exception\ExceptionHandler::handleException()
(/home/test/public_html/libraries/src/Application/CMSApplication.php:311)
at Joomla\CMS\Application\CMSApplication->execute()
(/home/test/public_html/includes/app.php:63)
at require_once('/home/test/public_html/includes/app.php')
(/home/test/public_html/index.php:32)

And in the backend

in /home/test/public_html/libraries/vendor/joomla/session/src/Storage/NativeStorage.php (line 473)

Failed to start the session because headers have already been sent by "/home/test/public_html/libraries/src/Application/WebApplication.php" at line 355.

NativeStorage->start()
in /home/test/public_html/libraries/src/Session/Storage/JoomlaStorage.php (line 305)
$this->setId($session_clean); $cookie->set($session_name, '', time() - 3600); } } parent::start(); // Try loading data from the session if (isset($_SESSION['joomla']) && !empty($_SESSION['joomla'])) { $this->data = unserialize(base64_decode($_SESSION['joomla']));

RuntimeException:
Failed to start the session because headers have already been sent by "/home/test/public_html/libraries/src/Application/WebApplication.php" at line 355.

at /home/test/public_html/libraries/vendor/joomla/session/src/Storage/NativeStorage.php:473
at Joomla\Session\Storage\NativeStorage->start()
(/home/test/public_html/libraries/src/Session/Storage/JoomlaStorage.php:305)
at Joomla\CMS\Session\Storage\JoomlaStorage->start()
(/home/test/public_html/libraries/vendor/joomla/session/src/Session.php:405)
at Joomla\Session\Session->start()
(/home/test/public_html/libraries/vendor/joomla/session/src/Session.php:332)
at Joomla\Session\Session->has()
(/home/test/public_html/libraries/src/Session/Session.php:201)
at Joomla\CMS\Session\Session->get()
(/home/test/public_html/libraries/src/Factory.php:338)
at Joomla\CMS\Factory::getUser()
(/home/test/public_html/libraries/src/Application/AdministratorApplication.php:229)
at Joomla\CMS\Application\AdministratorApplication->getTemplate()
(/home/test/public_html/libraries/src/Error/Renderer/HtmlRenderer.php:47)
at Joomla\CMS\Error\Renderer\HtmlRenderer->render()
(/home/test/public_html/libraries/src/Exception/ExceptionHandler.php:128)
at Joomla\CMS\Exception\ExceptionHandler::render()
(/home/test/public_html/libraries/src/Exception/ExceptionHandler.php:71)
at Joomla\CMS\Exception\ExceptionHandler::handleException()
(/home/test/public_html/libraries/src/Application/CMSApplication.php:311)
at Joomla\CMS\Application\CMSApplication->execute()
(/home/test/public_html/administrator/includes/app.php:63)
at require_once('/home/test/public_html/administrator/includes/app.php')
(/home/test/public_html/administrator/index.php:32)

Expected result

Actual result

System information (as much as possible)

Additional comments