Update to Drupal 8.2.0. For more information, see https://www.drupal.org/project/drupal/releases/8.2.0

core/modules/file/tests/file_test/file_test.module

@@ -317,7 +317,7 @@ function file_test_validator(File $file, $errors) {
  * When the function is called with no $filepath parameter, the results are
  * returned.
  *
- * @param string|NULL $filepath
+ * @param string|null $filepath
  *   File path
  * @return array
  *   If $filepath is NULL, an array of all previous $filepath parameters

core/modules/file/tests/file_test/src/StreamWrapper/DummyRemoteReadOnlyStreamWrapper.php

@@ -0,0 +1,33 @@
+<?php
+
+namespace Drupal\file_test\StreamWrapper;
+
+use Drupal\Core\StreamWrapper\StreamWrapperInterface;
+
+/**
+ * Dummy read-only remote stream wrapper (dummy-remote-readonly://).
+ */
+class DummyRemoteReadOnlyStreamWrapper extends DummyRemoteStreamWrapper {
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function getType() {
+    return StreamWrapperInterface::READ_VISIBLE;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getName() {
+    return t('Dummy remote read-only files');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getDescription() {
+    return t('Dummy remote read-only stream wrapper for testing.');
+  }
+
+}