only in patch2:
unchanged:
--- a/core/modules/ckeditor/src/Plugin/Editor/CKEditor.php
+++ b/core/modules/ckeditor/src/Plugin/Editor/CKEditor.php
@@ -405,7 +405,10 @@ public function buildContentsCssJSSetting(EditorEntity $editor) {
       drupal_get_path('module', 'system') . '/css/system.module.css',
     );
     $this->moduleHandler->alter('ckeditor_css', $css, $editor);
-    $css = array_merge($css, _ckeditor_theme_css());
+    $theme_css = _ckeditor_theme_css();
+    if (isset($theme_css)) {
+      $css = array_merge($css, $theme_css);
+    }
     $css = array_map('file_create_url', $css);
 
     return array_values($css);
only in patch2:
unchanged:
--- a/core/modules/quickedit/quickedit.module
+++ b/core/modules/quickedit/quickedit.module
@@ -77,7 +77,7 @@ function quickedit_library_info_alter(&$libraries, $extension) {
 
     // First let the base theme modify the library, then the actual theme.
     $alter_library = function(&$library, $theme) use (&$alter_library) {
-      if ($theme_path = drupal_get_path('theme', $theme)) {
+      if (isset($theme) && $theme_path = drupal_get_path('theme', $theme)) {
         $info = system_get_info('theme', $theme);
         // Recurse to process base theme(s) first.
         if (isset($info['base theme'])) {