Fixes #4204: `yii\web\Request::getUserIP()` will return null if it cannot detect user IP address

framework/CHANGELOG.md

@@ -427,6 +427,7 @@ Yii Framework 2 Change Log
 - Chg #2912: Relative view files will be looked for under the directory containing the view currently being rendered (qiangxue)
 - Chg #2955: Changed the signature of ActiveQuery constructors and replaced `ActiveRecord::createQuery()` with `find()` to simplify customizing ActiveQuery classes (qiangxue)
 - Chg #2999: Added `findOne()` and `findAll()` to replace the usage of `ActiveRecord::find($condition)`. (samdark, qiangxue)
+- Chg #4204: `yii\web\Request::getUserIP()` will return null if it cannot detect user IP address (qiangxue)
 - Chg: Renamed `yii\jui\Widget::clientEventsMap` to `clientEventMap` (qiangxue)
 - Chg: Renamed `ActiveRecord::getPopulatedRelations()` to `getRelatedRecords()` (qiangxue)
 - Chg: Renamed `attributeName` and `className` to `targetAttribute` and `targetClass` for `UniqueValidator` and `ExistValidator` (qiangxue)

framework/web/Request.php

@@ -829,11 +829,11 @@ class Request extends \yii\base\Request
 
     /**
      * Returns the user IP address.
-     * @return string user IP address
+     * @return string user IP address. Null is returned if the user IP address cannot be detected.
      */
     public function getUserIP()
     {
-        return isset($_SERVER['REMOTE_ADDR']) ? $_SERVER['REMOTE_ADDR'] : '127.0.0.1';
+        return isset($_SERVER['REMOTE_ADDR']) ? $_SERVER['REMOTE_ADDR'] : null;
     }
 
     /**