In a situation where the OAuth2 flow fails, it should not generate a PHP warning.

Trace:

2023-02-01 10:32:51 web plugin_mediawiki_187: [a080c822553591090ce24cf7] /mediawiki/_oauth/Special:TuleapLogin/callback?state=f9daf7b68e64f8205b3403d214edf83b&code=tlp-oauth2-ac1-72.e50da471be8585a73ecfde3589c4ab6dc325c8bf26617b0e571d7353f0f65bdf   ErrorException from line 87 of /usr/share/mediawiki-tuleap-flavor/extensions/TuleapIntegration/src/TuleapConnection.php: PHP Warning: hash_equals(): Expected known_string to be a string, null given #0 [internal function]: MWExceptionHandler::handleError()
#1 /usr/share/mediawiki-tuleap-flavor/extensions/TuleapIntegration/src/TuleapConnection.php(87): hash_equals()
#2 /usr/share/mediawiki-tuleap-flavor/extensions/TuleapIntegration/src/Special/TuleapLogin.php(109): TuleapIntegration\TuleapConnection->obtainAccessToken()
#3 /usr/share/mediawiki-tuleap-flavor/extensions/TuleapIntegration/src/Special/TuleapLogin.php(75): TuleapIntegration\Special\TuleapLogin->callback()
#4 /usr/share/mediawiki-tuleap-flavor/includes/specialpage/SpecialPage.php(600): TuleapIntegration\Special\TuleapLogin->execute()
#5 /usr/share/mediawiki-tuleap-flavor/includes/specialpage/SpecialPageFactory.php(635): SpecialPage->run()
#6 /usr/share/mediawiki-tuleap-flavor/includes/MediaWiki.php(307): MediaWiki\SpecialPage\SpecialPageFactory->executePath()
#7 /usr/share/mediawiki-tuleap-flavor/includes/MediaWiki.php(947): MediaWiki->performRequest()
#8 /usr/share/mediawiki-tuleap-flavor/includes/MediaWiki.php(547): MediaWiki->main()
#9 /usr/share/mediawiki-tuleap-flavor/index.php(53): MediaWiki->run()
#10 /usr/share/mediawiki-tuleap-flavor/index.php(46): wfIndexMain()
#11 {main}