[BUGFIX] Fix the return type of getConfiguration

Classes/Service/ConfigurationService.php

@@ -49,9 +49,9 @@ class ConfigurationService implements SingletonInterface {
 	 * @param string $key
 	 * @param array $settings
 	 * @throws InvalidConfigurationTypeException
-	 * @return string
+	 * @return array|string|NULL
 	 */
-	public function getConfiguration($key, array $settings): string {
+	public function getConfiguration($key, array $settings) {
 		if (!$this->tsConfig) {
 			$configurationManager = GeneralUtility::makeInstance(ConfigurationManager::class);
 			$this->tsConfig = $configurationManager->getConfiguration(ConfigurationManagerInterface::CONFIGURATION_TYPE_FULL_TYPOSCRIPT);