Throw an error when the active theme is not found

modules/cms/classes/Controller.php

@@ -93,6 +93,9 @@ class Controller extends BaseController
     public function __construct($theme = null)
     {
         $this->theme = $theme ? $theme : Theme::getActiveTheme();
+        if (!$this->theme)
+            throw new CmsException(Lang::get('cms::lang.theme.active.not_found'));
+
         $this->assetPath = Config::get('cms.themesDir').'/'.$this->theme->getDirName();
         $this->router = new Router($this->theme);
         $this->initTwigEnvironment();

modules/cms/lang/en/lang.php

@@ -15,6 +15,7 @@ return [
     'theme' => [
         'active' => [
             'not_set' => "The active theme is not set.",
+            'not_found' => "The active theme is not found.",
         ],
         'edit' => [
             'not_set' => "The edit theme is not set.",