Fix #19322: Revert force setting value to empty string in case it's null in yii\validators\FilterValidator::validateAttribute()

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

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);
         }
     }

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'],
         ];
     }