TYPO3 Core

The extbase localization utility (TYPO3\CMS\Extbase\Utility\LocalizationUtility) generates an error if the site language is null.

Line 196: $siteLanguage = self::getCurrentSiteLanguage();

Sometimes site language will be null here.

Line 199: $languageKeys['languageKey'] = $siteLanguage->getTypo3Language();

function call on null will generate an exception.

So line 199 should be:

if ($siteLanguage) {
$languageKeys['languageKey'] = $siteLanguage->getTypo3Language();
}