error PHP Deprecated: Return type of yii\web\Session::getIterator()

[pamparam83]

FastCGI sent in stderr: "PHP message: PHP Deprecated:  Return type of yii\web\Session::getIterator() should either be compatible with IteratorAggregate::getIterator(): Traversable, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice in /app/vendor/yiisoft/yii2/web/Session.php on line 665PHP message: PHP Fatal error:  During inheritance of IteratorAggregate: Uncaught yii\base\ErrorException: Return type of yii\web\Session::getIterator() should either be compatible with IteratorAggregate::getIterator(): Traversable, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice in /app/vendor/yiisoft/yii2/web/Session.php:665
Stack trace:
#0 /app/vendor/yiisoft/yii2/web/Session.php(76): yii\base\ErrorHandler->handleError()
#1 /app/vendor/yiisoft/yii2/BaseYii.php(293): include('...')
#2 [internal function]: yii\BaseYii::autoload()
#3 /app/vendor/yiisoft/yii2/di/Container.php(508): ReflectionClass->__construct()
#4 /app/vendor/yiisoft/yii2/di/Container.php(386): yii\di\Container->getDependencies()
#5 /app/vendor/yiisoft/yii2/di/Container.php(171): yii\di\Container->build()
#6 /app/vendor/yiisoft/yii2/BaseYii.php(365): yii\di\Container->get()
#7 /app/vendor/yiisoft/yii2/di/ServiceLocator.php(137): yii\BaseYii::createObject()
#8 /app/vendor/yiisoft/yii2/base...PHP message: PHP Fatal error:  During inheritance of IteratorAggregate: Uncaught yii\base\ErrorException: Return type of yii\web\HeaderCollection::getIterator() should either be compatible with IteratorAggregate::getIterator(): Traversable, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice in /app/vendor/yiisoft/yii2/web/HeaderCollection.php:37
Stack trace:
#0 /app/vendor/yiisoft/yii2/web/HeaderCollection.php(23): yii\base\ErrorHandler->handleError()
#1 /app/vendor/yiisoft/yii2/BaseYii.php(293): include('...')
#2 /app/vendor/yiisoft/yii2/web/Request.php(362): yii\BaseYii::autoload()
#3 /app/vendor/yiisoft/yii2

Q	A
Yii version	2.0.43
PHP version	8.1
Operating system	ubuntu 20.04

[pamparam83]

I install yii2 base template and add in file web/index.php error_reporting(E_ALL);
How to fix it?

[samdark]

By adding #[\ReturnTypeWillChange] annotation.

[pamparam83]

I added this attribute in web/Seession, web/CookieCollection and base/Model
result
"PHP message: PHP Deprecated: Return type of yii\web\HeaderCollection::getIterator() should either be compatible with IteratorAggregate::getIterator(): Traversable, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice in /app/vendor/yiisoft/yii2/web/HeaderCollection.php on line 37PHP message: PHP Stack trace:PHP message: PHP 1. yii\base\ErrorHandler->handleException($exception = class yii\base\ErrorException { protected $message = 'class_exists(): Passing null to parameter #1 ($class) of type string is deprecated'; private string ${Exception}string = ''; protected $code = 8192; protected string $file = '/app/vendor/yiisoft/yii2-debug/src/panels/UserPanel.php'; protected int $line = 91; private array ${Exception}trace = [0 => [...], 1 => [...], 2 => [...], 3 => [...], 4 => [...], 5 => [...], 6 => [...], 7 => [...], 8 => [...], 9 => [...], 10 => [...], 11 => [...], 12 => [...], 13 => [...], 14 => [...], 15 => [...], 16 => [...], 17 => [...], 18 => [...], 19 => [...], 20 => [...], 21 => [...]]; private ?Throwable ${Exception}previous = NULL; protected int $severity = 8192; public $xdebug_message = '<tr><th align=\'left\' bgcolor=\'#f57900\' colspan="5"><span style=\'background-color: #cc0000; color: #fce94f; font-size: x-large;\'>( ! )</span> yii\\base\\ErrorException: class_exists(): Passing null to p...PHP message: PHP 2. yii\web\ErrorHandler->renderException($exception = class yii\base\ErrorException { protected $message = 'class_exists(): Passing null to parameter #1 ($class) of type string is deprecated'; private string ${Exception}string = ''; protected $code = 8192; protected string $file = '/app/vendor/yiisoft/yii2-debug/src/panels/UserPanel.php';

I'm disabled debugger
got errors from web / HeaderCollection.php
added attribute #[\ReturnTypeWillChange]
index page opened,
error on the contact page and login page

PHP Deprecated Warning 'yii \ base \ ErrorException' with message 'htmlspecialchars (): Passing null to parameter # 1 ($ string) of type string is deprecated'

in /app/vendor/yiisoft/yii2/helpers/BaseHtml.php:111 

[samdark]

Yes, there are many things to check. See #19041 where we work on it. You may help with pull requests.