Only load configuration into IO if IO is available

src/Composer/Repository/RepositoryFactory.php

@@ -93,7 +93,9 @@ class RepositoryFactory
     {
         if (!$config) {
             $config = Factory::createConfig($io);
-            $io->loadConfiguration($config);
+            if ($io) {
+                $io->loadConfiguration($config);
+            }
         }
         if (!$rm) {
             if (!$io) {