From 2874e070f3ad88c727b1335ba4f4515855bf5f64 Mon Sep 17 00:00:00 2001
From: Bizley <pawel@positive.codes>
Date: Thu, 24 Mar 2022 14:50:00 +0100
Subject: [PATCH] Fix #19322: Revert force setting value to empty string in
 case it's `null` in `yii\validators\FilterValidator::validateAttribute()`

---
 framework/CHANGELOG.md                   | 1 +
 framework/validators/FilterValidator.php | 3 ++-
 tests/framework/base/ModelTest.php       | 2 +-
 3 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/framework/CHANGELOG.md b/framework/CHANGELOG.md
index f5b7a2e698..5a7da0ef23 100644
--- a/framework/CHANGELOG.md
+++ b/framework/CHANGELOG.md
@@ -9,6 +9,7 @@ Yii Framework 2 Change Log
 - Bug #19291: Reset errors and validators in `yii\base\Model::__clone()` (WinterSilence)
 - Enh #19304: Add filtering validator `yii\validators\TrimValidator` (WinterSilence)
 - Enh #19309: Optimize `yii\base\Model::attributes()` (WinterSilence)
+- Bug #19322: Revert force setting value to empty string in case it's `null` in `yii\validators\FilterValidator::validateAttribute()` (bizley)
 
 
 2.0.45 February 11, 2022
diff --git a/framework/validators/FilterValidator.php b/framework/validators/FilterValidator.php
index b896e337ae..d24131a971 100644
--- a/framework/validators/FilterValidator.php
+++ b/framework/validators/FilterValidator.php
@@ -25,6 +25,8 @@ use yii\base\InvalidConfigException;
  * ```
  *
  * Many PHP functions qualify this signature (e.g. `trim()`).
+ * If the callback function requires non-null argument (important since PHP 8.1)
+ * remember to set [[skipOnEmpty]] to `true` otherwise you may trigger an error.
  *
  * To specify the filter, set [[filter]] property to be the callback.
  *
@@ -75,7 +77,6 @@ class FilterValidator extends Validator
     {
         $value = $model->$attribute;
         if (!$this->skipOnArray || !is_array($value)) {
-            $value = isset($value) ? $value : '';
             $model->$attribute = call_user_func($this->filter, $value);
         }
     }
diff --git a/tests/framework/base/ModelTest.php b/tests/framework/base/ModelTest.php
index 428f3fb1b9..dcd5e893f3 100644
--- a/tests/framework/base/ModelTest.php
+++ b/tests/framework/base/ModelTest.php
@@ -526,7 +526,7 @@ class ComplexModel1 extends Model
     {
         return [
             [['id'], 'required', 'except' => 'administration'],
-            [['name', 'description'], 'filter', 'filter' => 'trim'],
+            [['name', 'description'], 'filter', 'filter' => 'trim', 'skipOnEmpty' => true],
             [['is_disabled'], 'boolean', 'on' => 'administration'],
         ];
     }