diff --git a/setup/moduleinstallation/InstallationChoicesToModuleConverter.php b/setup/moduleinstallation/InstallationChoicesToModuleConverter.php
index ac283375f..9a1ace949 100644
--- a/setup/moduleinstallation/InstallationChoicesToModuleConverter.php
+++ b/setup/moduleinstallation/InstallationChoicesToModuleConverter.php
@@ -82,7 +82,7 @@ class InstallationChoicesToModuleConverter
 		return ModuleDiscovery::GetAllModules($aSearchDirs);
 	}
 
-	private function FindInstalledPackageModules(array $aPackageModules, array $aInstallationChoices, array $aInstallationDescription = null): array
+	private function FindInstalledPackageModules(array $aPackageModules, array $aInstallationChoices, ?array $aInstallationDescription = null): array
 	{
 		$aInstalledModules = [];