diff --git a/core/modules/aggregator/lib/Drupal/aggregator/Tests/ImportOpmlTest.php b/core/modules/aggregator/lib/Drupal/aggregator/Tests/ImportOpmlTest.php
index 7a9f463..631bc6e 100644
--- a/core/modules/aggregator/lib/Drupal/aggregator/Tests/ImportOpmlTest.php
+++ b/core/modules/aggregator/lib/Drupal/aggregator/Tests/ImportOpmlTest.php
@@ -53,7 +53,7 @@ function openImportForm() {
 
     $this->drupalGet('admin/config/services/aggregator/add/opml');
     $this->assertText('A single OPML document may contain a collection of many feeds.', 'Found OPML help text.');
-    $this->assertField('files[upload]', 'Found file upload field.');
+    $this->assertField('files[upload][]', 'Found file upload field.');
     $this->assertField('remote', 'Found Remote URL field.');
     $this->assertField('refresh', '', 'Found Refresh field.');
     $this->assertFieldByName("category[$cid]", $cid, 'Found category field.');
@@ -71,7 +71,7 @@ function validateImportFormFields() {
 
     $path = $this->getEmptyOpml();
     $edit = array(
-      'files[upload]' => $path,
+      'files[upload][]' => $path,
       'remote' => file_create_url($path),
     );
     $this->drupalPost('admin/config/services/aggregator/add/opml', $edit, t('Import'));
@@ -91,7 +91,7 @@ function validateImportFormFields() {
   function submitImportForm() {
     $before = db_query('SELECT COUNT(*) FROM {aggregator_feed}')->fetchField();
 
-    $form['files[upload]'] = $this->getInvalidOpml();
+    $form['files[upload][]'] = $this->getInvalidOpml();
     $this->drupalPost('admin/config/services/aggregator/add/opml', $form, t('Import'));
     $this->assertText(t('No new feed has been added.'), 'Attempting to upload invalid XML.');
 
@@ -119,7 +119,7 @@ function submitImportForm() {
     $feeds[1] = $this->getFeedEditArray();
     $feeds[2] = $this->getFeedEditArray();
     $edit = array(
-      'files[upload]' => $this->getValidOpml($feeds),
+      'files[upload][]' => $this->getValidOpml($feeds),
       'refresh'       => '900',
       'category[1]'   => $category,
     );
diff --git a/core/modules/comment/lib/Drupal/comment/Tests/CommentPreviewTest.php b/core/modules/comment/lib/Drupal/comment/Tests/CommentPreviewTest.php
index 13817df..d7ec0b4 100644
--- a/core/modules/comment/lib/Drupal/comment/Tests/CommentPreviewTest.php
+++ b/core/modules/comment/lib/Drupal/comment/Tests/CommentPreviewTest.php
@@ -48,7 +48,7 @@ function testCommentPreview() {
     $edit['signature[value]'] = '<a href="http://example.com/">' . $test_signature. '</a>';
     $edit['signature[format]'] = 'filtered_html';
     $image = current($this->drupalGetTestFiles('image'));
-    $edit['files[user_picture_und_0]'] = drupal_realpath($image->uri);
+    $edit['files[user_picture_und_0][]'] = drupal_realpath($image->uri);
     $this->drupalPost('user/' . $this->web_user->uid . '/edit', $edit, t('Save'));
 
     // As the web user, fill in the comment form and preview the comment.
diff --git a/core/modules/file/file.module b/core/modules/file/file.module
index e1bf021..c21aa1c 100644
--- a/core/modules/file/file.module
+++ b/core/modules/file/file.module
@@ -1228,7 +1228,7 @@ function file_managed_file_save_upload($element) {
     $files = array_filter($files);
     $fids = array_map(function($file) {return $file->fid;}, $files);
 
-    return array_combine($fids, $files);
+    return empty($files) ? array() : array_combine($fids, $files);
   }
 
   return array();
diff --git a/core/modules/locale/lib/Drupal/locale/Tests/LocaleExportTest.php b/core/modules/locale/lib/Drupal/locale/Tests/LocaleExportTest.php
index 7ae1bf7..4f2748b 100644
--- a/core/modules/locale/lib/Drupal/locale/Tests/LocaleExportTest.php
+++ b/core/modules/locale/lib/Drupal/locale/Tests/LocaleExportTest.php
@@ -55,7 +55,7 @@ function testExportTranslation() {
     file_put_contents($name, $this->getPoFile());
     $this->drupalPost('admin/config/regional/translate/import', array(
       'langcode' => 'fr',
-      'files[file]' => $name,
+      'files[file][]' => $name,
     ), t('Import'));
     drupal_unlink($name);
 
@@ -74,7 +74,7 @@ function testExportTranslation() {
     file_put_contents($name, $this->getCustomPoFile());
     $this->drupalPost('admin/config/regional/translate/import', array(
       'langcode' => 'fr',
-      'files[file]' => $name,
+      'files[file][]' => $name,
       'customized' => 1,
     ), t('Import'));
     drupal_unlink($name);
diff --git a/core/modules/locale/lib/Drupal/locale/Tests/LocaleImportFunctionalTest.php b/core/modules/locale/lib/Drupal/locale/Tests/LocaleImportFunctionalTest.php
index fd3667c..dcd7bf2 100644
--- a/core/modules/locale/lib/Drupal/locale/Tests/LocaleImportFunctionalTest.php
+++ b/core/modules/locale/lib/Drupal/locale/Tests/LocaleImportFunctionalTest.php
@@ -91,7 +91,7 @@ function testStandalonePoFile() {
     $name = $this->randomName(16);
     $this->drupalPost('admin/config/regional/translate/import', array(
       'langcode' => 'fr',
-      'files[file]' => $name,
+      'files[file][]' => $name,
     ), t('Import'));
     $this->assertEqual($this->getUrl(), url('admin/config/regional/translate/import', array('absolute' => TRUE)), t('Correct page redirection.'));
     $this->assertText(t('File to import not found.'), t('File to import not found message.'));
@@ -248,7 +248,7 @@ function testEmptyMsgstr() {
   function importPoFile($contents, array $options = array()) {
     $name = tempnam('temporary://', "po_") . '.po';
     file_put_contents($name, $contents);
-    $options['files[file]'] = $name;
+    $options['files[file][]'] = $name;
     $this->drupalPost('admin/config/regional/translate/import', $options, t('Import'));
     drupal_unlink($name);
   }
diff --git a/core/modules/locale/lib/Drupal/locale/Tests/LocalePluralFormatTest.php b/core/modules/locale/lib/Drupal/locale/Tests/LocalePluralFormatTest.php
index 8119199..069dc4e 100644
--- a/core/modules/locale/lib/Drupal/locale/Tests/LocalePluralFormatTest.php
+++ b/core/modules/locale/lib/Drupal/locale/Tests/LocalePluralFormatTest.php
@@ -268,7 +268,7 @@ function testPluralEditExport() {
   function importPoFile($contents, array $options = array()) {
     $name = tempnam('temporary://', "po_") . '.po';
     file_put_contents($name, $contents);
-    $options['files[file]'] = $name;
+    $options['files[file][]'] = $name;
     $this->drupalPost('admin/config/regional/translate/import', $options, t('Import'));
     drupal_unlink($name);
   }
diff --git a/core/modules/rdf/lib/Drupal/rdf/Tests/RdfaMarkupTest.php b/core/modules/rdf/lib/Drupal/rdf/Tests/RdfaMarkupTest.php
index 6f99dae..589ad4b 100644
--- a/core/modules/rdf/lib/Drupal/rdf/Tests/RdfaMarkupTest.php
+++ b/core/modules/rdf/lib/Drupal/rdf/Tests/RdfaMarkupTest.php
@@ -139,8 +139,8 @@ function testAttributesInMarkupFile() {
 
     // Create an array for drupalPost with the field names as the keys and
     // the URIs for the test files as the values.
-    $edit = array("files[" . $field_name . "_" . $langcode . "_0]" => drupal_realpath($file->uri),
-                  "files[" . $image_field . "_" . $langcode . "_0]" => drupal_realpath($image->uri));
+    $edit = array("files[" . $field_name . "_" . $langcode . "_0][]" => drupal_realpath($file->uri),
+                  "files[" . $image_field . "_" . $langcode . "_0][]" => drupal_realpath($image->uri));
 
     // Create node and save, then edit node to upload files.
     $node = $this->drupalCreateNode(array('type' => 'article', 'promote' => 1));
diff --git a/core/modules/system/lib/Drupal/system/Tests/Form/StateValuesCleanAdvancedTest.php b/core/modules/system/lib/Drupal/system/Tests/Form/StateValuesCleanAdvancedTest.php
index ceae2af..b7c8e22 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Form/StateValuesCleanAdvancedTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Form/StateValuesCleanAdvancedTest.php
@@ -47,7 +47,7 @@ function testFormStateValuesCleanAdvanced() {
     $this->assertTrue(is_file($this->image->uri), "The image file we're going to upload exists.");
 
     // "Browse" for the desired file.
-    $edit = array('files[image]' => drupal_realpath($this->image->uri));
+    $edit = array('files[image][]' => drupal_realpath($this->image->uri));
 
     // Post the form.
     $this->drupalPost('form_test/form-state-values-clean-advanced', $edit, t('Submit'));
diff --git a/core/modules/system/lib/Drupal/system/Tests/System/ThemeTest.php b/core/modules/system/lib/Drupal/system/Tests/System/ThemeTest.php
index 111e6b7..7e335e2 100644
--- a/core/modules/system/lib/Drupal/system/Tests/System/ThemeTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/System/ThemeTest.php
@@ -156,7 +156,7 @@ function testThemeSettings() {
     $edit = array(
       'default_logo' => FALSE,
       'logo_path' => '',
-      'files[logo_upload]' => drupal_realpath($file->uri),
+      'files[logo_upload][]' => drupal_realpath($file->uri),
     );
     $this->drupalPost('admin/appearance/settings', $edit, t('Save configuration'));
 
diff --git a/core/modules/update/lib/Drupal/update/Tests/UpdateUploadTest.php b/core/modules/update/lib/Drupal/update/Tests/UpdateUploadTest.php
index d3bcdb8..0a8db21 100644
--- a/core/modules/update/lib/Drupal/update/Tests/UpdateUploadTest.php
+++ b/core/modules/update/lib/Drupal/update/Tests/UpdateUploadTest.php
@@ -44,7 +44,7 @@ public function testUploadModule() {
     $imageTestFiles = $this->drupalGetTestFiles('image');
     $invalidArchiveFile = reset($imageTestFiles);
     $edit = array(
-      'files[project_upload]' => $invalidArchiveFile->uri,
+      'files[project_upload][]' => $invalidArchiveFile->uri,
     );
     // This also checks that the correct archive extensions are allowed.
     $this->drupalPost('admin/modules/install', $edit, t('Install'));
@@ -55,7 +55,7 @@ public function testUploadModule() {
     // installed until after extraction.
     $validArchiveFile = drupal_get_path('module', 'update') . '/tests/aaa_update_test.tar.gz';
     $edit = array(
-      'files[project_upload]' => $validArchiveFile,
+      'files[project_upload][]' => $validArchiveFile,
     );
     $this->drupalPost('admin/modules/install', $edit, t('Install'));
     $this->assertText(t('@module_name is already installed.', array('@module_name' => 'AAA Update test')), 'Existing module was extracted and not reinstalled.');
diff --git a/core/modules/user/lib/Drupal/user/Tests/UserPictureTest.php b/core/modules/user/lib/Drupal/user/Tests/UserPictureTest.php
index 8447031..fde2fbc 100644
--- a/core/modules/user/lib/Drupal/user/Tests/UserPictureTest.php
+++ b/core/modules/user/lib/Drupal/user/Tests/UserPictureTest.php
@@ -117,7 +117,7 @@ function testPictureOnNodeComment() {
    * Edits the user picture for the test user.
    */
   function saveUserPicture($image) {
-    $edit = array('files[user_picture_und_0]' => drupal_realpath($image->uri));
+    $edit = array('files[user_picture_und_0][]' => drupal_realpath($image->uri));
     $this->drupalPost('user/' . $this->web_user->uid . '/edit', $edit, t('Save'));
 
     // Load actual user data from database.