Fixes #5806: Allow `Html::encode()` to be used when the application is not started

framework/CHANGELOG.md

@@ -25,6 +25,7 @@ Yii Framework 2 Change Log
 - Enh #5613: Added `--overwrite` option to Gii console command to support overwriting all files (motin, qiangxue)
 - Enh #5646: Call `yii\base\ErrorHandler::unregister()` instead of `restore_*_handlers` directly (aivus)
 - Enh #5735: Added `yii\bootstrap\Tabs::renderTabContent` to support manually rendering tab contents (RomeroMsk)
+- Enh #5806: Allow `Html::encode()` to be used when the application is not started (qiangxue)
 - Enh: `Console::confirm()` now uses `Console::stdout()` instead of `echo` to be consistent with all other functions (cebe)
 - Chg #3630: `yii\db\Command::queryInternal()` is now protected (samdark) 
 - Chg #5508: Dropped the support for the `--append` option for the `fixture` command (qiangxue) 

framework/helpers/BaseHtml.php

@@ -93,7 +93,7 @@ class BaseHtml
      */
     public static function encode($content, $doubleEncode = true)
     {
-        return htmlspecialchars($content, ENT_QUOTES | ENT_SUBSTITUTE, Yii::$app->charset, $doubleEncode);
+        return htmlspecialchars($content, ENT_QUOTES | ENT_SUBSTITUTE, Yii::$app ? Yii::$app->charset : 'UTF-8', $doubleEncode);
     }
 
     /**