Issue #3182941: Stop assuming a request always exists

Closes #3182941

src/Flysystem/S3.php

@@ -159,12 +159,14 @@ class S3 implements FlysystemPluginInterface, ContainerFactoryPluginInterface {
    *   The Flysystem configuration.
    */
   public static function mergeConfiguration(ContainerInterface $container, array $configuration) {
-    $protocol = $container->get('request_stack')
-      ->getCurrentRequest()
-      ->getScheme();
+    $request = $container->get('request_stack')
+      ->getCurrentRequest();
 
-    return $configuration += [
-      'protocol' => $protocol,
+    if ($request && !isset($configuration['protocol'])) {
+      $configuration['protocol'] = $request->getScheme();
+    }
+
+    return $configuration + [
       'region' => 'us-east-1',
       'endpoint' => NULL,
     ];