[BUG] PHP 8: Warning in ext_getSetup aborts indexing

[saitho]

Describe the bug
Fetching nested TypoScript setup via ApacheSolrForTypo3\Solr\FrontendEnvironment\TypoScript::ext_getSetup(array $theSetup, string $theKey) results the following warning during indexing via backend:

TYPO3\CMS\Core\Error\Exception: Warning: Undefined array key "tx_myextension" in /var/www/html/public/typo3conf/ext/solr/Classes/FrontendEnvironment/TypoScript.php line 129 in /var/www/html/vendor/helhum/typo3-console/Classes/Console/Error/ErrorHandler.php:88
Stack trace:
#0 /var/www/html/public/typo3conf/ext/solr/Classes/FrontendEnvironment/TypoScript.php(129): Helhum\Typo3Console\Error\ErrorHandler->handleError(2, 'Undefined array...', '/var/www/html/p...', 129)
#1 /var/www/html/public/typo3conf/ext/solr/Classes/FrontendEnvironment/TypoScript.php(127): ApacheSolrForTypo3\Solr\FrontendEnvironment\TypoScript->ext_getSetup(Array, 'tx_myextension')
#2 /var/www/html/public/typo3conf/ext/solr/Classes/FrontendEnvironment/TypoScript.php(113): ApacheSolrForTypo3\Solr\FrontendEnvironment\TypoScript->ext_getSetup(Array, 'plugin.tx_myext...')
#3 /var/www/html/public/typo3conf/ext/solr/Classes/FrontendEnvironment/TypoScript.php(85): ApacheSolrForTypo3\Solr\FrontendEnvironment\TypoScript->buildConfigurationArray(1, 'plugin.tx_myext...', 0)
#4 /var/www/html/public/typo3conf/ext/solr/Classes/FrontendEnvironment.php(52): ApacheSolrForTypo3\Solr\FrontendEnvironment\TypoScript->getConfigurationFromPageId(1, 'plugin.tx_myext...', 0, NULL)
#5 /var/www/html/public/typo3conf/ext/tx_myextension/Classes/Helper/SolrHelper.php(253): ApacheSolrForTypo3\Solr\FrontendEnvironment->getConfigurationFromPageId(1, 'plugin.tx_myext...', 0)

This warning then results in an error during indexing.

To Reproduce

TypoScript setup:

plugin.tx_myextension {
  settings {
    foo = bar
  }
}

Snipped, placed inside a Solr indexer or Solr indexer hook:

use ApacheSolrForTypo3\Solr\FrontendEnvironment;

// @var $indexItem \ApacheSolrForTypo3\Solr\IndexQueue\Item

$settings =  GeneralUtility::makeInstance(FrontendEnvironment::class)
  ->getConfigurationFromPageId($indexItem->getRootPageUid(), 'plugin.tx_myextension', 0);
$config = $settings->getObjectByPathOrDefault('settings', []);
// $config should return the array ['foo' => 'bar']

Expected behavior

Missing value assignments to TypoScript structures should be ignored, defaulting to an empty string
as the original method of TYPO3 v11 does:
https://github.com/TYPO3/typo3/blob/11.5/typo3/sysext/core/Classes/TypoScript/ExtendedTemplateService.php#L304

Used versions (please complete the following information):

• TYPO3 Version: 11.5.16
• EXT:solr Version: 11.5.0
• PHP Version: 8.1.8