diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index b30366e..47259a1 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -33,7 +33,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu-latest]
-        php: ['5.4', '5.5', '5.6', '7.0', '7.1', '7.2', '7.3', '7.4', '8.0']
+        php: ['5.4', '5.5', '5.6', '7.0', '7.1', '7.2', '7.3', '7.4', '8.0', '8.1']
 
     steps:
       - name: Generate french locale
diff --git a/composer.json b/composer.json
index 84af41a..240a682 100644
--- a/composer.json
+++ b/composer.json
@@ -118,9 +118,13 @@
             "phpunit/phpunit-mock-objects": {
                 "Fix PHP 7 and 8 compatibility": "https://yiisoft.github.io/phpunit-patches/phpunit_mock_objects.patch"
             },
+            "phpunit/php-file-iterator": {
+                "Fix PHP 8.1 compatibility": "https://yiisoft.github.io/phpunit-patches/phpunit_path_file_iterator.patch"
+            },
             "phpunit/phpunit": {
                 "Fix PHP 7 compatibility": "https://yiisoft.github.io/phpunit-patches/phpunit_php7.patch",
-                "Fix PHP 8 compatibility": "https://yiisoft.github.io/phpunit-patches/phpunit_php8.patch"
+                "Fix PHP 8 compatibility": "https://yiisoft.github.io/phpunit-patches/phpunit_php8.patch",
+                "Fix PHP 8.1 compatibility": "https://yiisoft.github.io/phpunit-patches/phpunit_php81.patch"
             }
         }
     }
diff --git a/composer.lock b/composer.lock
index 35d4dd1..6d56b84 100644
--- a/composer.lock
+++ b/composer.lock
@@ -4,7 +4,7 @@
         "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#installing-dependencies",
         "This file is @generated automatically"
     ],
-    "content-hash": "8f9a4d7e645592f806605d32d676f54e",
+    "content-hash": "1dd00a91030b984d98f13fa6d6ecf7d9",
     "packages": [
         {
             "name": "bower-asset/inputmask",
@@ -1338,16 +1338,16 @@
         },
         {
             "name": "phpunit/phpunit",
-            "version": "4.8.34",
+            "version": "4.8.36",
             "source": {
                 "type": "git",
                 "url": "https://github.com/sebastianbergmann/phpunit.git",
-                "reference": "7eb45205d27edd94bd2b3614085ea158bd1e2bca"
+                "reference": "46023de9a91eec7dfb06cc56cb4e260017298517"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/sebastianbergmann/phpunit/zipball/7eb45205d27edd94bd2b3614085ea158bd1e2bca",
-                "reference": "7eb45205d27edd94bd2b3614085ea158bd1e2bca",
+                "url": "https://api.github.com/repos/sebastianbergmann/phpunit/zipball/46023de9a91eec7dfb06cc56cb4e260017298517",
+                "reference": "46023de9a91eec7dfb06cc56cb4e260017298517",
                 "shasum": ""
             },
             "require": {
@@ -1408,9 +1408,9 @@
             ],
             "support": {
                 "issues": "https://github.com/sebastianbergmann/phpunit/issues",
-                "source": "https://github.com/sebastianbergmann/phpunit/tree/4.8.34"
+                "source": "https://github.com/sebastianbergmann/phpunit/tree/4.8.36"
             },
-            "time": "2017-01-26T16:15:36+00:00"
+            "time": "2017-06-21T08:07:12+00:00"
         },
         {
             "name": "phpunit/phpunit-mock-objects",
diff --git a/framework/BaseYii.php b/framework/BaseYii.php
index 0aa00f7..8814e32 100644
--- a/framework/BaseYii.php
+++ b/framework/BaseYii.php
@@ -130,7 +130,7 @@ class BaseYii
      */
     public static function getAlias($alias, $throwException = true)
     {
-        if (strncmp($alias, '@', 1) !== 0) {
+        if (strncmp((string)$alias, '@', 1) !== 0) {
             // not an alias
             return $alias;
         }
diff --git a/framework/CHANGELOG.md b/framework/CHANGELOG.md
index ddf4b51..4f8b839 100644
--- a/framework/CHANGELOG.md
+++ b/framework/CHANGELOG.md
@@ -5,6 +5,7 @@ Yii Framework 2 Change Log
 ------------------------
 
 - Bug #19138: Allow digits in language code (ntesic)
+- Bug #19041: Fix PHP 8.1 issues (longthanhtran, samdark, pamparam83, sartor, githubjeka)
 
 
 2.0.44 December 30, 2021
diff --git a/framework/base/ArrayAccessTrait.php b/framework/base/ArrayAccessTrait.php
index 87a1db1..9c632bc 100644
--- a/framework/base/ArrayAccessTrait.php
+++ b/framework/base/ArrayAccessTrait.php
@@ -26,6 +26,7 @@ trait ArrayAccessTrait
      * It will be implicitly called when you use `foreach` to traverse the collection.
      * @return \ArrayIterator an iterator for traversing the cookies in the collection.
      */
+    #[\ReturnTypeWillChange]
     public function getIterator()
     {
         return new \ArrayIterator($this->data);
@@ -36,6 +37,7 @@ trait ArrayAccessTrait
      * This method is required by Countable interface.
      * @return int number of data elements.
      */
+    #[\ReturnTypeWillChange]
     public function count()
     {
         return count($this->data);
@@ -46,6 +48,7 @@ trait ArrayAccessTrait
      * @param mixed $offset the offset to check on
      * @return bool
      */
+    #[\ReturnTypeWillChange]
     public function offsetExists($offset)
     {
         return isset($this->data[$offset]);
@@ -56,6 +59,7 @@ trait ArrayAccessTrait
      * @param int $offset the offset to retrieve element.
      * @return mixed the element at the offset, null if no element is found at the offset
      */
+    #[\ReturnTypeWillChange]
     public function offsetGet($offset)
     {
         return isset($this->data[$offset]) ? $this->data[$offset] : null;
@@ -66,6 +70,7 @@ trait ArrayAccessTrait
      * @param int $offset the offset to set element
      * @param mixed $item the element value
      */
+    #[\ReturnTypeWillChange]
     public function offsetSet($offset, $item)
     {
         $this->data[$offset] = $item;
@@ -75,6 +80,7 @@ trait ArrayAccessTrait
      * This method is required by the interface [[\ArrayAccess]].
      * @param mixed $offset the offset to unset element
      */
+    #[\ReturnTypeWillChange]
     public function offsetUnset($offset)
     {
         unset($this->data[$offset]);
diff --git a/framework/base/ExitException.php b/framework/base/ExitException.php
index 4fde6a8..fe9f5e7 100644
--- a/framework/base/ExitException.php
+++ b/framework/base/ExitException.php
@@ -33,6 +33,10 @@ class ExitException extends \Exception
     public function __construct($status = 0, $message = null, $code = 0, $previous = null)
     {
         $this->statusCode = $status;
-        parent::__construct($message, $code, $previous);
+        if ($previous === null) {
+            parent::__construct((string)$message, $code);
+        } else {
+            parent::__construct((string)$message, $code, $previous);
+        }
     }
 }
diff --git a/framework/base/Model.php b/framework/base/Model.php
index e957a96..40c820e 100644
--- a/framework/base/Model.php
+++ b/framework/base/Model.php
@@ -995,6 +995,7 @@ class Model extends Component implements StaticInstanceInterface, IteratorAggreg
      * This method is required by the interface [[\IteratorAggregate]].
      * @return ArrayIterator an iterator for traversing the items in the list.
      */
+    #[\ReturnTypeWillChange]
     public function getIterator()
     {
         $attributes = $this->getAttributes();
@@ -1008,6 +1009,7 @@ class Model extends Component implements StaticInstanceInterface, IteratorAggreg
      * @param string $offset the offset to check on.
      * @return bool whether or not an offset exists.
      */
+    #[\ReturnTypeWillChange]
     public function offsetExists($offset)
     {
         return isset($this->$offset);
@@ -1020,6 +1022,7 @@ class Model extends Component implements StaticInstanceInterface, IteratorAggreg
      * @param string $offset the offset to retrieve element.
      * @return mixed the element at the offset, null if no element is found at the offset
      */
+    #[\ReturnTypeWillChange]
     public function offsetGet($offset)
     {
         return $this->$offset;
@@ -1032,6 +1035,7 @@ class Model extends Component implements StaticInstanceInterface, IteratorAggreg
      * @param string $offset the offset to set element
      * @param mixed $value the element value
      */
+    #[\ReturnTypeWillChange]
     public function offsetSet($offset, $value)
     {
         $this->$offset = $value;
@@ -1043,6 +1047,7 @@ class Model extends Component implements StaticInstanceInterface, IteratorAggreg
      * It is implicitly called when you use something like `unset($model[$offset])`.
      * @param string $offset the offset to unset element
      */
+    #[\ReturnTypeWillChange]
     public function offsetUnset($offset)
     {
         $this->$offset = null;
diff --git a/framework/base/Security.php b/framework/base/Security.php
index 6276bf5..5c86ad8 100644
--- a/framework/base/Security.php
+++ b/framework/base/Security.php
@@ -298,7 +298,7 @@ class Security extends Component
     public function hkdf($algo, $inputKey, $salt = null, $info = null, $length = 0)
     {
         if (function_exists('hash_hkdf')) {
-            $outputKey = hash_hkdf($algo, $inputKey, $length, $info, $salt);
+            $outputKey = hash_hkdf((string)$algo, (string)$inputKey, $length, (string)$info, (string)$salt);
             if ($outputKey === false) {
                 throw new InvalidArgumentException('Invalid parameters to hash_hkdf()');
             }
diff --git a/framework/caching/Cache.php b/framework/caching/Cache.php
index a4afaee..dd2ae4e 100644
--- a/framework/caching/Cache.php
+++ b/framework/caching/Cache.php
@@ -526,6 +526,7 @@ abstract class Cache extends Component implements CacheInterface
      * @param string $key a key identifying the cached value
      * @return bool
      */
+    #[\ReturnTypeWillChange]
     public function offsetExists($key)
     {
         return $this->get($key) !== false;
@@ -537,6 +538,7 @@ abstract class Cache extends Component implements CacheInterface
      * @param string $key a key identifying the cached value
      * @return mixed the value stored in cache, false if the value is not in the cache or expired.
      */
+    #[\ReturnTypeWillChange]
     public function offsetGet($key)
     {
         return $this->get($key);
@@ -550,6 +552,7 @@ abstract class Cache extends Component implements CacheInterface
      * @param string $key the key identifying the value to be cached
      * @param mixed $value the value to be cached
      */
+    #[\ReturnTypeWillChange]
     public function offsetSet($key, $value)
     {
         $this->set($key, $value);
@@ -560,6 +563,7 @@ abstract class Cache extends Component implements CacheInterface
      * This method is required by the interface [[\ArrayAccess]].
      * @param string $key the key of the value to be deleted
      */
+    #[\ReturnTypeWillChange]
     public function offsetUnset($key)
     {
         $this->delete($key);
diff --git a/framework/console/controllers/HelpController.php b/framework/console/controllers/HelpController.php
index f61875f..a6e2cf0 100644
--- a/framework/console/controllers/HelpController.php
+++ b/framework/console/controllers/HelpController.php
@@ -473,8 +473,8 @@ class HelpController extends Controller
      */
     protected function formatOptionHelp($name, $required, $type, $defaultValue, $comment)
     {
-        $comment = trim($comment);
-        $type = trim($type);
+        $comment = trim((string)$comment);
+        $type = trim((string)$type);
         if (strncmp($type, 'bool', 4) === 0) {
             $type = 'boolean, 0 or 1';
         }
diff --git a/framework/db/ArrayExpression.php b/framework/db/ArrayExpression.php
index e473eb1..9cb1830 100644
--- a/framework/db/ArrayExpression.php
+++ b/framework/db/ArrayExpression.php
@@ -104,6 +104,7 @@ class ArrayExpression implements ExpressionInterface, \ArrayAccess, \Countable,
      * The return value will be casted to boolean if non-boolean was returned.
      * @since 2.0.14
      */
+    #[\ReturnTypeWillChange]
     public function offsetExists($offset)
     {
         return isset($this->value[$offset]);
@@ -119,6 +120,7 @@ class ArrayExpression implements ExpressionInterface, \ArrayAccess, \Countable,
      * @return mixed Can return all value types.
      * @since 2.0.14
      */
+    #[\ReturnTypeWillChange]
     public function offsetGet($offset)
     {
         return $this->value[$offset];
@@ -137,6 +139,7 @@ class ArrayExpression implements ExpressionInterface, \ArrayAccess, \Countable,
      * @return void
      * @since 2.0.14
      */
+    #[\ReturnTypeWillChange]
     public function offsetSet($offset, $value)
     {
         $this->value[$offset] = $value;
@@ -152,6 +155,7 @@ class ArrayExpression implements ExpressionInterface, \ArrayAccess, \Countable,
      * @return void
      * @since 2.0.14
      */
+    #[\ReturnTypeWillChange]
     public function offsetUnset($offset)
     {
         unset($this->value[$offset]);
@@ -167,6 +171,7 @@ class ArrayExpression implements ExpressionInterface, \ArrayAccess, \Countable,
      * The return value is cast to an integer.
      * @since 2.0.14
      */
+    #[\ReturnTypeWillChange]
     public function count()
     {
         return count($this->value);
@@ -181,6 +186,7 @@ class ArrayExpression implements ExpressionInterface, \ArrayAccess, \Countable,
      * @since 2.0.14.1
      * @throws InvalidConfigException when ArrayExpression contains QueryInterface object
      */
+    #[\ReturnTypeWillChange]
     public function getIterator()
     {
         $value = $this->getValue();
diff --git a/framework/db/BaseActiveRecord.php b/framework/db/BaseActiveRecord.php
index 8ae0602..747ac1f 100644
--- a/framework/db/BaseActiveRecord.php
+++ b/framework/db/BaseActiveRecord.php
@@ -1219,6 +1219,7 @@ abstract class BaseActiveRecord extends Model implements ActiveRecordInterface
      * @param mixed $offset the offset to check on
      * @return bool whether there is an element at the specified offset.
      */
+    #[\ReturnTypeWillChange]
     public function offsetExists($offset)
     {
         return $this->__isset($offset);
diff --git a/framework/db/BatchQueryResult.php b/framework/db/BatchQueryResult.php
index c473d0e..749a57a 100644
--- a/framework/db/BatchQueryResult.php
+++ b/framework/db/BatchQueryResult.php
@@ -114,6 +114,7 @@ class BatchQueryResult extends Component implements \Iterator
      * Resets the iterator to the initial state.
      * This method is required by the interface [[\Iterator]].
      */
+    #[\ReturnTypeWillChange]
     public function rewind()
     {
         $this->reset();
@@ -124,6 +125,7 @@ class BatchQueryResult extends Component implements \Iterator
      * Moves the internal pointer to the next dataset.
      * This method is required by the interface [[\Iterator]].
      */
+    #[\ReturnTypeWillChange]
     public function next()
     {
         if ($this->_batch === null || !$this->each || $this->each && next($this->_batch) === false) {
@@ -197,6 +199,7 @@ class BatchQueryResult extends Component implements \Iterator
      * This method is required by the interface [[\Iterator]].
      * @return int the index of the current row.
      */
+    #[\ReturnTypeWillChange]
     public function key()
     {
         return $this->_key;
@@ -207,6 +210,7 @@ class BatchQueryResult extends Component implements \Iterator
      * This method is required by the interface [[\Iterator]].
      * @return mixed the current dataset.
      */
+    #[\ReturnTypeWillChange]
     public function current()
     {
         return $this->_value;
@@ -217,6 +221,7 @@ class BatchQueryResult extends Component implements \Iterator
      * This method is required by the interface [[\Iterator]].
      * @return bool whether there is a valid dataset at the current position.
      */
+    #[\ReturnTypeWillChange]
     public function valid()
     {
         return !empty($this->_batch);
diff --git a/framework/db/Connection.php b/framework/db/Connection.php
index 65fb8f7..6d13565 100644
--- a/framework/db/Connection.php
+++ b/framework/db/Connection.php
@@ -736,6 +736,11 @@ class Connection extends Component
                 $this->pdo->setAttribute(PDO::ATTR_EMULATE_PREPARES, $this->emulatePrepare);
             }
         }
+
+        if (PHP_VERSION_ID >= 80100 && $this->getDriverName() === 'sqlite') {
+            $this->pdo->setAttribute(PDO::ATTR_STRINGIFY_FETCHES, true);
+        }
+
         if (!$this->isSybase && in_array($this->getDriverName(), ['mssql', 'dblib'], true)) {
             $this->pdo->exec('SET ANSI_NULL_DFLT_ON ON');
         }
@@ -1004,7 +1009,7 @@ class Connection extends Component
     public function getDriverName()
     {
         if ($this->_driverName === null) {
-            if (($pos = strpos($this->dsn, ':')) !== false) {
+            if (($pos = strpos((string)$this->dsn, ':')) !== false) {
                 $this->_driverName = strtolower(substr($this->dsn, 0, $pos));
             } else {
                 $this->_driverName = strtolower($this->getSlavePdo()->getAttribute(PDO::ATTR_DRIVER_NAME));
diff --git a/framework/db/DataReader.php b/framework/db/DataReader.php
index 99427f9..d533fd9 100644
--- a/framework/db/DataReader.php
+++ b/framework/db/DataReader.php
@@ -196,6 +196,7 @@ class DataReader extends \yii\base\BaseObject implements \Iterator, \Countable
      * In this case, use "SELECT COUNT(*) FROM tableName" to obtain the number of rows.
      * @return int number of rows contained in the result.
      */
+    #[\ReturnTypeWillChange]
     public function count()
     {
         return $this->getRowCount();
@@ -216,6 +217,7 @@ class DataReader extends \yii\base\BaseObject implements \Iterator, \Countable
      * This method is required by the interface [[\Iterator]].
      * @throws InvalidCallException if this method is invoked twice
      */
+    #[\ReturnTypeWillChange]
     public function rewind()
     {
         if ($this->_index < 0) {
@@ -231,6 +233,7 @@ class DataReader extends \yii\base\BaseObject implements \Iterator, \Countable
      * This method is required by the interface [[\Iterator]].
      * @return int the index of the current row.
      */
+    #[\ReturnTypeWillChange]
     public function key()
     {
         return $this->_index;
@@ -241,6 +244,7 @@ class DataReader extends \yii\base\BaseObject implements \Iterator, \Countable
      * This method is required by the interface [[\Iterator]].
      * @return mixed the current row.
      */
+    #[\ReturnTypeWillChange]
     public function current()
     {
         return $this->_row;
@@ -250,6 +254,7 @@ class DataReader extends \yii\base\BaseObject implements \Iterator, \Countable
      * Moves the internal pointer to the next row.
      * This method is required by the interface [[\Iterator]].
      */
+    #[\ReturnTypeWillChange]
     public function next()
     {
         $this->_row = $this->_statement->fetch();
@@ -261,6 +266,7 @@ class DataReader extends \yii\base\BaseObject implements \Iterator, \Countable
      * This method is required by the interface [[\Iterator]].
      * @return bool whether there is a row of data at current position.
      */
+    #[\ReturnTypeWillChange]
     public function valid()
     {
         return $this->_row !== false;
diff --git a/framework/db/JsonExpression.php b/framework/db/JsonExpression.php
index 36b4603..9ee3967 100644
--- a/framework/db/JsonExpression.php
+++ b/framework/db/JsonExpression.php
@@ -86,6 +86,7 @@ class JsonExpression implements ExpressionInterface, \JsonSerializable
      * @since 2.0.14.2
      * @throws InvalidConfigException when JsonExpression contains QueryInterface object
      */
+    #[\ReturnTypeWillChange]
     public function jsonSerialize()
     {
         $value = $this->getValue();
diff --git a/framework/db/Query.php b/framework/db/Query.php
index 857339f..fc614f7 100644
--- a/framework/db/Query.php
+++ b/framework/db/Query.php
@@ -921,7 +921,7 @@ PATTERN;
      */
     public function andFilterCompare($name, $value, $defaultOperator = '=')
     {
-        if (preg_match('/^(<>|>=|>|<=|<|=)/', $value, $matches)) {
+        if (preg_match('/^(<>|>=|>|<=|<|=)/', (string)$value, $matches)) {
             $operator = $matches[1];
             $value = substr($value, strlen($operator));
         } else {
diff --git a/framework/db/SqlToken.php b/framework/db/SqlToken.php
index 2fc46d8..be15525 100644
--- a/framework/db/SqlToken.php
+++ b/framework/db/SqlToken.php
@@ -83,6 +83,7 @@ class SqlToken extends BaseObject implements \ArrayAccess
      * @param int $offset child token offset.
      * @return bool whether the token exists.
      */
+    #[\ReturnTypeWillChange]
     public function offsetExists($offset)
     {
         return isset($this->_children[$this->calculateOffset($offset)]);
@@ -95,6 +96,7 @@ class SqlToken extends BaseObject implements \ArrayAccess
      * @param int $offset child token offset.
      * @return SqlToken|null the child token at the specified offset, `null` if there's no token.
      */
+    #[\ReturnTypeWillChange]
     public function offsetGet($offset)
     {
         $offset = $this->calculateOffset($offset);
@@ -108,6 +110,7 @@ class SqlToken extends BaseObject implements \ArrayAccess
      * @param int|null $offset child token offset.
      * @param SqlToken $token token to be added.
      */
+    #[\ReturnTypeWillChange]
     public function offsetSet($offset, $token)
     {
         $token->parent = $this;
@@ -125,6 +128,7 @@ class SqlToken extends BaseObject implements \ArrayAccess
      * It is implicitly called when you use something like `unset($token[$offset])`.
      * @param int $offset child token offset.
      */
+    #[\ReturnTypeWillChange]
     public function offsetUnset($offset)
     {
         $offset = $this->calculateOffset($offset);
diff --git a/framework/db/mysql/Schema.php b/framework/db/mysql/Schema.php
index 90ecd31..87ae9ad 100644
--- a/framework/db/mysql/Schema.php
+++ b/framework/db/mysql/Schema.php
@@ -297,7 +297,7 @@ SQL;
                 && preg_match('/^current_timestamp(?:\(([0-9]*)\))?$/i', $info['default'], $matches)) {
                 $column->defaultValue = new Expression('CURRENT_TIMESTAMP' . (!empty($matches[1]) ? '(' . $matches[1] . ')' : ''));
             } elseif (isset($type) && $type === 'bit') {
-                $column->defaultValue = bindec(trim($info['default'], 'b\''));
+                $column->defaultValue = bindec(trim(isset($info['default']) ? $info['default'] : '', 'b\''));
             } else {
                 $column->defaultValue = $column->phpTypecast($info['default']);
             }
diff --git a/framework/grid/Column.php b/framework/grid/Column.php
index 465a855..829747e 100644
--- a/framework/grid/Column.php
+++ b/framework/grid/Column.php
@@ -26,7 +26,7 @@ class Column extends BaseObject
      */
     public $grid;
     /**
-     * @var string the header cell content. Note that it will not be HTML-encoded.
+     * @var null|string the header cell content. Note that it will not be HTML-encoded.
      */
     public $header;
     /**
@@ -127,7 +127,7 @@ class Column extends BaseObject
      */
     protected function renderHeaderCellContent()
     {
-        return trim($this->header) !== '' ? $this->header : $this->getHeaderCellLabel();
+        return $this->header !== null && trim($this->header) !== '' ? $this->header : $this->getHeaderCellLabel();
     }
 
     /**
@@ -149,7 +149,7 @@ class Column extends BaseObject
      */
     protected function renderFooterCellContent()
     {
-        return trim($this->footer) !== '' ? $this->footer : $this->grid->emptyCell;
+        return $this->footer !== null && trim($this->footer) !== '' ? $this->footer : $this->grid->emptyCell;
     }
 
     /**
diff --git a/framework/helpers/BaseConsole.php b/framework/helpers/BaseConsole.php
index 2852762..fe84a88 100644
--- a/framework/helpers/BaseConsole.php
+++ b/framework/helpers/BaseConsole.php
@@ -331,7 +331,7 @@ class BaseConsole
      */
     public static function stripAnsiFormat($string)
     {
-        return preg_replace(self::ansiCodesPattern(), '', $string);
+        return preg_replace(self::ansiCodesPattern(), '', (string)$string);
     }
 
     /**
@@ -370,9 +370,9 @@ class BaseConsole
             return '';
         }
 
-        $textItems = preg_split(self::ansiCodesPattern(), $string);
+        $textItems = preg_split(self::ansiCodesPattern(), (string)$string);
 
-        preg_match_all(self::ansiCodesPattern(), $string, $colors);
+        preg_match_all(self::ansiCodesPattern(), (string)$string, $colors);
         $colors = count($colors) ? $colors[0] : [];
         array_unshift($colors, '');
 
diff --git a/framework/helpers/BaseFileHelper.php b/framework/helpers/BaseFileHelper.php
index a9c2434..fbd8059 100644
--- a/framework/helpers/BaseFileHelper.php
+++ b/framework/helpers/BaseFileHelper.php
@@ -161,6 +161,11 @@ class BaseFileHelper
 
             throw new InvalidConfigException('The fileinfo PHP extension is not installed.');
         }
+
+        if (PHP_VERSION_ID >= 80100) {
+            return static::getMimeTypeByExtension($file, $magicFile);
+        }
+
         $info = finfo_open(FILEINFO_MIME_TYPE, $magicFile);
 
         if ($info) {
@@ -900,7 +905,7 @@ class BaseFileHelper
      */
     public static function changeOwnership($path, $ownership, $mode = null)
     {
-        if (!file_exists($path)) {
+        if (!file_exists((string)$path)) {
             throw new InvalidArgumentException('Unable to change ownerhip, "' . $path . '" is not a file or directory.');
         }
 
diff --git a/framework/helpers/BaseHtml.php b/framework/helpers/BaseHtml.php
index 1e66c31..0a9d905 100644
--- a/framework/helpers/BaseHtml.php
+++ b/framework/helpers/BaseHtml.php
@@ -115,7 +115,7 @@ class BaseHtml
      */
     public static function encode($content, $doubleEncode = true)
     {
-        return htmlspecialchars($content, ENT_QUOTES | ENT_SUBSTITUTE, Yii::$app ? Yii::$app->charset : 'UTF-8', $doubleEncode);
+        return htmlspecialchars((string)$content, ENT_QUOTES | ENT_SUBSTITUTE, Yii::$app ? Yii::$app->charset : 'UTF-8', $doubleEncode);
     }
 
     /**
diff --git a/framework/helpers/BaseStringHelper.php b/framework/helpers/BaseStringHelper.php
index 738147e..3c1e0ff 100644
--- a/framework/helpers/BaseStringHelper.php
+++ b/framework/helpers/BaseStringHelper.php
@@ -29,7 +29,7 @@ class BaseStringHelper
      */
     public static function byteLength($string)
     {
-        return mb_strlen($string, '8bit');
+        return mb_strlen((string)$string, '8bit');
     }
 
     /**
@@ -148,7 +148,7 @@ class BaseStringHelper
             return static::truncateHtml($string, $count, $suffix);
         }
 
-        $words = preg_split('/(\s+)/u', trim($string), null, PREG_SPLIT_DELIM_CAPTURE);
+        $words = preg_split('/(\s+)/u', trim($string), 0, PREG_SPLIT_DELIM_CAPTURE);
         if (count($words) / 2 > $count) {
             return implode('', array_slice($words, 0, ($count * 2) - 1)) . $suffix;
         }
@@ -316,7 +316,7 @@ class BaseStringHelper
      */
     public static function countWords($string)
     {
-        return count(preg_split('/\s+/u', $string, null, PREG_SPLIT_NO_EMPTY));
+        return count(preg_split('/\s+/u', $string, 0, PREG_SPLIT_NO_EMPTY));
     }
 
     /**
@@ -436,7 +436,7 @@ class BaseStringHelper
             $pattern .= 'i';
         }
 
-        return preg_match($pattern, $string) === 1;
+        return preg_match($pattern, (string)$string) === 1;
     }
 
     /**
@@ -450,8 +450,8 @@ class BaseStringHelper
      */
     public static function mb_ucfirst($string, $encoding = 'UTF-8')
     {
-        $firstChar = mb_substr($string, 0, 1, $encoding);
-        $rest = mb_substr($string, 1, null, $encoding);
+        $firstChar = mb_substr((string)$string, 0, 1, $encoding);
+        $rest = mb_substr((string)$string, 1, null, $encoding);
 
         return mb_strtoupper($firstChar, $encoding) . $rest;
     }
diff --git a/framework/i18n/GettextMoFile.php b/framework/i18n/GettextMoFile.php
index 43b5afa..f632d2d 100644
--- a/framework/i18n/GettextMoFile.php
+++ b/framework/i18n/GettextMoFile.php
@@ -106,7 +106,7 @@ class GettextMoFile extends GettextFile
         $messages = [];
         for ($i = 0; $i < $count; ++$i) {
             $id = $this->readString($fileHandle, $sourceLengths[$i], $sourceOffsets[$i]);
-            $separatorPosition = strpos($id, chr(4));
+            $separatorPosition = strpos((string)$id, chr(4));
 
 
             if ((!$context && $separatorPosition === false) || ($context && $separatorPosition !== false && strncmp($id, $context, $separatorPosition) === 0)) {
diff --git a/framework/i18n/PhpMessageSource.php b/framework/i18n/PhpMessageSource.php
index dc9f2cf..92dfa1b 100644
--- a/framework/i18n/PhpMessageSource.php
+++ b/framework/i18n/PhpMessageSource.php
@@ -72,7 +72,7 @@ class PhpMessageSource extends MessageSource
         $messageFile = $this->getMessageFilePath($category, $language);
         $messages = $this->loadMessagesFromFile($messageFile);
 
-        $fallbackLanguage = substr($language, 0, 2);
+        $fallbackLanguage = substr((string)$language, 0, 2);
         $fallbackSourceLanguage = substr($this->sourceLanguage, 0, 2);
 
         if ($fallbackLanguage !== '' && $language !== $fallbackLanguage) {
diff --git a/framework/mail/BaseMailer.php b/framework/mail/BaseMailer.php
index 63b6904..1b20058 100644
--- a/framework/mail/BaseMailer.php
+++ b/framework/mail/BaseMailer.php
@@ -342,8 +342,9 @@ abstract class BaseMailer extends Component implements MailerInterface, ViewCont
     public function generateMessageFileName()
     {
         $time = microtime(true);
+        $timeInt = (int) $time;
 
-        return date('Ymd-His-', $time) . sprintf('%04d', (int) (($time - (int) $time) * 10000)) . '-' . sprintf('%04d', random_int(0, 10000)) . '.eml';
+        return date('Ymd-His-', $timeInt) . sprintf('%04d', (int) (($time - $timeInt) * 10000)) . '-' . sprintf('%04d', random_int(0, 10000)) . '.eml';
     }
 
     /**
diff --git a/framework/rest/UrlRule.php b/framework/rest/UrlRule.php
index d90ccf5..e1a0e2f 100644
--- a/framework/rest/UrlRule.php
+++ b/framework/rest/UrlRule.php
@@ -62,7 +62,7 @@ use yii\web\UrlRuleInterface;
 class UrlRule extends CompositeUrlRule
 {
     /**
-     * @var string the common prefix string shared by all patterns.
+     * @var string|null the common prefix string shared by all patterns.
      */
     public $prefix;
     /**
@@ -158,7 +158,7 @@ class UrlRule extends CompositeUrlRule
         }
         $this->controller = $controllers;
 
-        $this->prefix = trim($this->prefix, '/');
+        $this->prefix = trim((string)$this->prefix, '/');
 
         parent::init();
     }
diff --git a/framework/validators/FileValidator.php b/framework/validators/FileValidator.php
index b86b6c4..b094821 100644
--- a/framework/validators/FileValidator.php
+++ b/framework/validators/FileValidator.php
@@ -188,7 +188,7 @@ class FileValidator extends Validator
             $this->tooSmall = Yii::t('yii', 'The file "{file}" is too small. Its size cannot be smaller than {formattedLimit}.');
         }
         if (!is_array($this->extensions)) {
-            $this->extensions = preg_split('/[\s,]+/', strtolower($this->extensions), -1, PREG_SPLIT_NO_EMPTY);
+            $this->extensions = preg_split('/[\s,]+/', strtolower((string)$this->extensions), -1, PREG_SPLIT_NO_EMPTY);
         } else {
             $this->extensions = array_map('strtolower', $this->extensions);
         }
@@ -196,7 +196,7 @@ class FileValidator extends Validator
             $this->wrongMimeType = Yii::t('yii', 'Only files with these MIME types are allowed: {mimeTypes}.');
         }
         if (!is_array($this->mimeTypes)) {
-            $this->mimeTypes = preg_split('/[\s,]+/', strtolower($this->mimeTypes), -1, PREG_SPLIT_NO_EMPTY);
+            $this->mimeTypes = preg_split('/[\s,]+/', strtolower((string)$this->mimeTypes), -1, PREG_SPLIT_NO_EMPTY);
         } else {
             $this->mimeTypes = array_map('strtolower', $this->mimeTypes);
         }
diff --git a/framework/validators/FilterValidator.php b/framework/validators/FilterValidator.php
index 873e1b1..b896e33 100644
--- a/framework/validators/FilterValidator.php
+++ b/framework/validators/FilterValidator.php
@@ -75,6 +75,7 @@ class FilterValidator extends Validator
     {
         $value = $model->$attribute;
         if (!$this->skipOnArray || !is_array($value)) {
+            $value = isset($value) ? $value : '';
             $model->$attribute = call_user_func($this->filter, $value);
         }
     }
diff --git a/framework/web/CookieCollection.php b/framework/web/CookieCollection.php
index 2e9bef2..938c2b7 100644
--- a/framework/web/CookieCollection.php
+++ b/framework/web/CookieCollection.php
@@ -54,6 +54,7 @@ class CookieCollection extends BaseObject implements \IteratorAggregate, \ArrayA
      * It will be implicitly called when you use `foreach` to traverse the collection.
      * @return ArrayIterator an iterator for traversing the cookies in the collection.
      */
+    #[\ReturnTypeWillChange]
     public function getIterator()
     {
         return new ArrayIterator($this->_cookies);
@@ -65,6 +66,7 @@ class CookieCollection extends BaseObject implements \IteratorAggregate, \ArrayA
      * It will be implicitly called when you use `count($collection)`.
      * @return int the number of cookies in the collection.
      */
+    #[\ReturnTypeWillChange]
     public function count()
     {
         return $this->getCount();
@@ -198,6 +200,7 @@ class CookieCollection extends BaseObject implements \IteratorAggregate, \ArrayA
      * @param string $name the cookie name
      * @return bool whether the named cookie exists
      */
+    #[\ReturnTypeWillChange]
     public function offsetExists($name)
     {
         return $this->has($name);
@@ -211,6 +214,7 @@ class CookieCollection extends BaseObject implements \IteratorAggregate, \ArrayA
      * @param string $name the cookie name
      * @return Cookie the cookie with the specified name, null if the named cookie does not exist.
      */
+    #[\ReturnTypeWillChange]
     public function offsetGet($name)
     {
         return $this->get($name);
@@ -224,6 +228,7 @@ class CookieCollection extends BaseObject implements \IteratorAggregate, \ArrayA
      * @param string $name the cookie name
      * @param Cookie $cookie the cookie to be added
      */
+    #[\ReturnTypeWillChange]
     public function offsetSet($name, $cookie)
     {
         $this->add($cookie);
@@ -236,6 +241,7 @@ class CookieCollection extends BaseObject implements \IteratorAggregate, \ArrayA
      * This is equivalent to [[remove()]].
      * @param string $name the cookie name
      */
+    #[\ReturnTypeWillChange]
     public function offsetUnset($name)
     {
         $this->remove($name);
diff --git a/framework/web/GroupUrlRule.php b/framework/web/GroupUrlRule.php
index 4ce3b19..7ad9965 100644
--- a/framework/web/GroupUrlRule.php
+++ b/framework/web/GroupUrlRule.php
@@ -77,7 +77,7 @@ class GroupUrlRule extends CompositeUrlRule
      */
     public function init()
     {
-        $this->prefix = trim($this->prefix, '/');
+        $this->prefix = trim((string)$this->prefix);
         $this->routePrefix = $this->routePrefix === null ? $this->prefix : trim($this->routePrefix, '/');
         parent::init();
     }
diff --git a/framework/web/HeaderCollection.php b/framework/web/HeaderCollection.php
index b7a3324..737e2b5 100644
--- a/framework/web/HeaderCollection.php
+++ b/framework/web/HeaderCollection.php
@@ -33,6 +33,7 @@ class HeaderCollection extends BaseObject implements \IteratorAggregate, \ArrayA
      * It will be implicitly called when you use `foreach` to traverse the collection.
      * @return \ArrayIterator an iterator for traversing the headers in the collection.
      */
+    #[\ReturnTypeWillChange]
     public function getIterator()
     {
         return new \ArrayIterator($this->_headers);
@@ -44,6 +45,7 @@ class HeaderCollection extends BaseObject implements \IteratorAggregate, \ArrayA
      * It will be implicitly called when you use `count($collection)`.
      * @return int the number of headers in the collection.
      */
+    #[\ReturnTypeWillChange]
     public function count()
     {
         return $this->getCount();
@@ -53,6 +55,7 @@ class HeaderCollection extends BaseObject implements \IteratorAggregate, \ArrayA
      * Returns the number of headers in the collection.
      * @return int the number of headers in the collection.
      */
+    #[\ReturnTypeWillChange]
     public function getCount()
     {
         return count($this->_headers);
@@ -64,7 +67,7 @@ class HeaderCollection extends BaseObject implements \IteratorAggregate, \ArrayA
      * @param mixed $default the value to return in case the named header does not exist
      * @param bool $first whether to only return the first header of the specified name.
      * If false, all headers of the specified name will be returned.
-     * @return string|array the named header(s). If `$first` is true, a string will be returned;
+     * @return string|array|null the named header(s). If `$first` is true, a string will be returned;
      * If `$first` is false, an array will be returned.
      */
     public function get($name, $default = null, $first = true)
@@ -189,6 +192,7 @@ class HeaderCollection extends BaseObject implements \IteratorAggregate, \ArrayA
      * @param string $name the header name
      * @return bool whether the named header exists
      */
+    #[\ReturnTypeWillChange]
     public function offsetExists($name)
     {
         return $this->has($name);
@@ -202,6 +206,7 @@ class HeaderCollection extends BaseObject implements \IteratorAggregate, \ArrayA
      * @param string $name the header name
      * @return string the header value with the specified name, null if the named header does not exist.
      */
+    #[\ReturnTypeWillChange]
     public function offsetGet($name)
     {
         return $this->get($name);
@@ -215,6 +220,7 @@ class HeaderCollection extends BaseObject implements \IteratorAggregate, \ArrayA
      * @param string $name the header name
      * @param string $value the header value to be added
      */
+    #[\ReturnTypeWillChange]
     public function offsetSet($name, $value)
     {
         $this->set($name, $value);
@@ -227,6 +233,7 @@ class HeaderCollection extends BaseObject implements \IteratorAggregate, \ArrayA
      * This is equivalent to [[remove()]].
      * @param string $name the header name
      */
+    #[\ReturnTypeWillChange]
     public function offsetUnset($name)
     {
         $this->remove($name);
diff --git a/framework/web/HttpException.php b/framework/web/HttpException.php
index f7f6ac5..15ad444 100644
--- a/framework/web/HttpException.php
+++ b/framework/web/HttpException.php
@@ -45,7 +45,7 @@ class HttpException extends UserException
     public function __construct($status, $message = null, $code = 0, \Exception $previous = null)
     {
         $this->statusCode = $status;
-        parent::__construct($message, $code, $previous);
+        parent::__construct((string)$message, $code, $previous);
     }
 
     /**
diff --git a/framework/web/Request.php b/framework/web/Request.php
index 3d41c9e..a7511be 100644
--- a/framework/web/Request.php
+++ b/framework/web/Request.php
@@ -564,7 +564,7 @@ class Request extends \yii\base\Request
             }
 
             $rawContentType = $this->getContentType();
-            if (($pos = strpos($rawContentType, ';')) !== false) {
+            if (($pos = strpos((string)$rawContentType, ';')) !== false) {
                 // e.g. text/html; charset=UTF-8
                 $contentType = substr($rawContentType, 0, $pos);
             } else {
@@ -790,7 +790,7 @@ class Request extends \yii\base\Request
     public function getHostName()
     {
         if ($this->_hostName === null) {
-            $this->_hostName = parse_url($this->getHostInfo(), PHP_URL_HOST);
+            $this->_hostName = parse_url((string)$this->getHostInfo(), PHP_URL_HOST);
         }
 
         return $this->_hostName;
@@ -1467,7 +1467,7 @@ class Request extends \yii\base\Request
      * contained in [[getRawBody()]] or, in the case of the HEAD method, the
      * media type that would have been sent had the request been a GET.
      * For the MIME-types the user expects in response, see [[acceptableContentTypes]].
-     * @return string request content-type. Null is returned if this information is not available.
+     * @return string request content-type. Empty string is returned if this information is not available.
      * @link https://tools.ietf.org/html/rfc2616#section-14.17
      * HTTP 1.1 header field definitions
      */
@@ -1478,7 +1478,7 @@ class Request extends \yii\base\Request
         }
 
         //fix bug https://bugs.php.net/bug.php?id=66606
-        return $this->headers->get('Content-Type');
+        return $this->headers->get('Content-Type') ?: '';
     }
 
     private $_languages;
diff --git a/framework/web/Response.php b/framework/web/Response.php
index 4928eaf..eebb0cc 100644
--- a/framework/web/Response.php
+++ b/framework/web/Response.php
@@ -892,7 +892,7 @@ class Response extends \yii\base\Response
 
         if ($checkAjax) {
             if ($request->getIsAjax()) {
-                if (in_array($statusCode, [301, 302]) && preg_match('/Trident\/|MSIE[ ]/', $request->userAgent)) {
+                if (in_array($statusCode, [301, 302]) && preg_match('/Trident\/|MSIE[ ]/', (string)$request->userAgent)) {
                     $statusCode = 200;
                 }
                 if ($request->getIsPjax()) {
diff --git a/framework/web/Session.php b/framework/web/Session.php
index e121ea1..118a7e8 100644
--- a/framework/web/Session.php
+++ b/framework/web/Session.php
@@ -660,6 +660,7 @@ class Session extends Component implements \IteratorAggregate, \ArrayAccess, \Co
      * This method is required by the interface [[\IteratorAggregate]].
      * @return SessionIterator an iterator for traversing the session variables.
      */
+    #[\ReturnTypeWillChange]
     public function getIterator()
     {
         $this->open();
@@ -681,6 +682,7 @@ class Session extends Component implements \IteratorAggregate, \ArrayAccess, \Co
      * This method is required by [[\Countable]] interface.
      * @return int number of items in the session.
      */
+    #[\ReturnTypeWillChange]
     public function count()
     {
         return $this->getCount();
@@ -962,6 +964,7 @@ class Session extends Component implements \IteratorAggregate, \ArrayAccess, \Co
      * @param int|string $offset the offset to check on
      * @return bool
      */
+    #[\ReturnTypeWillChange]
     public function offsetExists($offset)
     {
         $this->open();
@@ -974,6 +977,7 @@ class Session extends Component implements \IteratorAggregate, \ArrayAccess, \Co
      * @param int|string $offset the offset to retrieve element.
      * @return mixed the element at the offset, null if no element is found at the offset
      */
+    #[\ReturnTypeWillChange]
     public function offsetGet($offset)
     {
         $this->open();
@@ -986,6 +990,7 @@ class Session extends Component implements \IteratorAggregate, \ArrayAccess, \Co
      * @param int|string $offset the offset to set element
      * @param mixed $item the element value
      */
+    #[\ReturnTypeWillChange]
     public function offsetSet($offset, $item)
     {
         $this->open();
@@ -996,6 +1001,7 @@ class Session extends Component implements \IteratorAggregate, \ArrayAccess, \Co
      * This method is required by the interface [[\ArrayAccess]].
      * @param int|string $offset the offset to unset element
      */
+    #[\ReturnTypeWillChange]
     public function offsetUnset($offset)
     {
         $this->open();
diff --git a/framework/web/UrlNormalizerRedirectException.php b/framework/web/UrlNormalizerRedirectException.php
index 88147cf..ed33f9f 100644
--- a/framework/web/UrlNormalizerRedirectException.php
+++ b/framework/web/UrlNormalizerRedirectException.php
@@ -47,6 +47,6 @@ class UrlNormalizerRedirectException extends \yii\base\Exception
         $this->url = $url;
         $this->scheme = $scheme;
         $this->statusCode = $statusCode;
-        parent::__construct($message, $code, $previous);
+        parent::__construct((string)$message, $code, $previous);
     }
 }
diff --git a/framework/web/UrlRule.php b/framework/web/UrlRule.php
index f5c96e8..673c2d6 100644
--- a/framework/web/UrlRule.php
+++ b/framework/web/UrlRule.php
@@ -79,7 +79,7 @@ class UrlRule extends BaseObject implements UrlRuleInterface
      */
     public $pattern;
     /**
-     * @var string the pattern used to parse and create the host info part of a URL (e.g. `http://example.com`).
+     * @var string|null the pattern used to parse and create the host info part of a URL (e.g. `http://example.com`).
      * @see pattern
      */
     public $host;
@@ -336,7 +336,7 @@ class UrlRule extends BaseObject implements UrlRuleInterface
         $this->pattern = '#^' . trim(strtr($this->_template, $tr), '/') . '$#u';
 
         // if host starts with relative scheme, then insert pattern to match any
-        if (strncmp($this->host, '//', 2) === 0) {
+        if ($this->host !== null && strncmp($this->host, '//', 2) === 0) {
             $this->pattern = substr_replace($this->pattern, '[\w]+://', 2, 0);
         }
 
diff --git a/tests/data/base/ArrayAccessObject.php b/tests/data/base/ArrayAccessObject.php
index bf62ef2..1fe0b34 100644
--- a/tests/data/base/ArrayAccessObject.php
+++ b/tests/data/base/ArrayAccessObject.php
@@ -29,6 +29,7 @@ class ArrayAccessObject extends TraversableObject implements \ArrayAccess
      * The return value will be casted to boolean if non-boolean was returned.
      * @since 2.0.14.1
      */
+    #[\ReturnTypeWillChange]
     public function offsetExists($offset)
     {
         return isset($this->data[$offset]);
@@ -44,6 +45,7 @@ class ArrayAccessObject extends TraversableObject implements \ArrayAccess
      * @return mixed Can return all value types.
      * @since 2.0.14.1
      */
+    #[\ReturnTypeWillChange]
     public function offsetGet($offset)
     {
         return $this->data[$offset];
@@ -62,6 +64,7 @@ class ArrayAccessObject extends TraversableObject implements \ArrayAccess
      * @return void
      * @since 2.0.14.1
      */
+    #[\ReturnTypeWillChange]
     public function offsetSet($offset, $value)
     {
         $this->data[$offset] = $value;
@@ -77,6 +80,7 @@ class ArrayAccessObject extends TraversableObject implements \ArrayAccess
      * @return void
      * @since 2.0.14.1
      */
+    #[\ReturnTypeWillChange]
     public function offsetUnset($offset)
     {
         unset($this->data[$offset]);
diff --git a/tests/data/base/TraversableObject.php b/tests/data/base/TraversableObject.php
index c8686b1..037fe73 100644
--- a/tests/data/base/TraversableObject.php
+++ b/tests/data/base/TraversableObject.php
@@ -28,6 +28,7 @@ class TraversableObject implements \Iterator, \Countable
      * @throws \Exception
      * @since 5.1.0
      */
+    #[\ReturnTypeWillChange]
     public function count()
     {
         throw new \Exception('Count called on object that should only be traversed.');
@@ -36,6 +37,7 @@ class TraversableObject implements \Iterator, \Countable
     /**
      * {@inheritdoc}
      */
+    #[\ReturnTypeWillChange]
     public function current()
     {
         return $this->data[$this->position];
@@ -44,6 +46,7 @@ class TraversableObject implements \Iterator, \Countable
     /**
      * {@inheritdoc}
      */
+    #[\ReturnTypeWillChange]
     public function next()
     {
         $this->position++;
@@ -52,6 +55,7 @@ class TraversableObject implements \Iterator, \Countable
     /**
      * {@inheritdoc}
      */
+    #[\ReturnTypeWillChange]
     public function key()
     {
         return $this->position;
@@ -60,6 +64,7 @@ class TraversableObject implements \Iterator, \Countable
     /**
      * {@inheritdoc}
      */
+    #[\ReturnTypeWillChange]
     public function valid()
     {
         return array_key_exists($this->position, $this->data);
@@ -68,6 +73,7 @@ class TraversableObject implements \Iterator, \Countable
     /**
      * {@inheritdoc}
      */
+    #[\ReturnTypeWillChange]
     public function rewind()
     {
         $this->position = 0;
diff --git a/tests/framework/base/SecurityTest.php b/tests/framework/base/SecurityTest.php
index 215999c..70b958c 100644
--- a/tests/framework/base/SecurityTest.php
+++ b/tests/framework/base/SecurityTest.php
@@ -1046,7 +1046,12 @@ TEXT;
      */
     public function testHkdf($hash, $ikm, $salt, $info, $l, $prk, $okm)
     {
-        $dk = $this->security->hkdf($hash, hex2bin($ikm), hex2bin($salt), hex2bin($info), $l);
+        $dk = $this->security->hkdf(
+            (string)$hash,
+            hex2bin((string)$ikm),
+            hex2bin((string)$salt),
+            hex2bin((string)$info),
+            $l);
         $this->assertEquals($okm, bin2hex($dk));
     }
 
diff --git a/tests/framework/caching/MemCachedTest.php b/tests/framework/caching/MemCachedTest.php
index 78f6678..c71a019 100644
--- a/tests/framework/caching/MemCachedTest.php
+++ b/tests/framework/caching/MemCachedTest.php
@@ -27,6 +27,12 @@ class MemCachedTest extends CacheTestCase
             $this->markTestSkipped('memcached not installed. Skipping.');
         }
 
+        if (PHP_VERSION_ID >= 80100 && version_compare(phpversion('memcached'), '3.1.5', '<=')) {
+            $php_version = phpversion();
+            $memcached_version = phpversion('memcached');
+            $this->markTestSkipped("memcached version $memcached_version is not ready for PHP $php_version. Skipping.");
+        }
+
         // check whether memcached is running and skip tests if not.
         if (!@stream_socket_client('127.0.0.1:11211', $errorNumber, $errorDescription, 0.5)) {
             $this->markTestSkipped('No memcached server running at ' . '127.0.0.1:11211' . ' : ' . $errorNumber . ' - ' . $errorDescription);
diff --git a/tests/framework/filters/auth/BasicAuthTest.php b/tests/framework/filters/auth/BasicAuthTest.php
index f5d5524..498f145 100644
--- a/tests/framework/filters/auth/BasicAuthTest.php
+++ b/tests/framework/filters/auth/BasicAuthTest.php
@@ -78,7 +78,7 @@ class BasicAuthTest extends AuthTest
         $filter = [
             'class' => HttpBasicAuth::className(),
             'auth' => function ($username, $password) {
-                if (preg_match('/\d$/', $username)) {
+                if (preg_match('/\d$/', (string)$username)) {
                     return UserIdentity::findIdentity($username);
                 }
 
diff --git a/tests/framework/helpers/ArrayHelperTest.php b/tests/framework/helpers/ArrayHelperTest.php
index 614d074..11f6ead 100644
--- a/tests/framework/helpers/ArrayHelperTest.php
+++ b/tests/framework/helpers/ArrayHelperTest.php
@@ -1477,6 +1477,7 @@ class ArrayAccessibleObject implements ArrayAccess
         $this->container = $container;
     }
 
+    #[\ReturnTypeWillChange]
     public function offsetSet($offset, $value)
     {
         if (is_null($offset)) {
@@ -1486,16 +1487,19 @@ class ArrayAccessibleObject implements ArrayAccess
         }
     }
 
+    #[\ReturnTypeWillChange]
     public function offsetExists($offset)
     {
         return array_key_exists($offset, $this->container);
     }
 
+    #[\ReturnTypeWillChange]
     public function offsetUnset($offset)
     {
         unset($this->container[$offset]);
     }
 
+    #[\ReturnTypeWillChange]
     public function offsetGet($offset)
     {
         return $this->offsetExists($offset) ? $this->container[$offset] : null;
@@ -1519,26 +1523,31 @@ class TraversableArrayAccessibleObject extends ArrayAccessibleObject implements
         return array_key_exists($keyIndex, $keys) ? $keys[$keyIndex] : false;
     }
 
+    #[\ReturnTypeWillChange]
     public function rewind()
     {
         $this->position = 0;
     }
 
+    #[\ReturnTypeWillChange]
     public function current()
     {
         return $this->offsetGet($this->getContainerKey($this->position));
     }
 
+    #[\ReturnTypeWillChange]
     public function key()
     {
         return $this->getContainerKey($this->position);
     }
 
+    #[\ReturnTypeWillChange]
     public function next()
     {
         ++$this->position;
     }
 
+    #[\ReturnTypeWillChange]
     public function valid()
     {
         $key = $this->getContainerKey($this->position);
diff --git a/tests/framework/models/JsonModel.php b/tests/framework/models/JsonModel.php
index f30dfce..89c43ef 100644
--- a/tests/framework/models/JsonModel.php
+++ b/tests/framework/models/JsonModel.php
@@ -24,6 +24,7 @@ class JsonModel extends DynamicModel implements \JsonSerializable
     /**
      * @return array
      */
+    #[\ReturnTypeWillChange]
     public function jsonSerialize()
     {
         return $this->data;
diff --git a/tests/framework/rest/SerializerTest.php b/tests/framework/rest/SerializerTest.php
index 6fd7097..b88c09c 100644
--- a/tests/framework/rest/SerializerTest.php
+++ b/tests/framework/rest/SerializerTest.php
@@ -540,6 +540,7 @@ class TestModel3 extends Model implements \JsonSerializable
         return static::$extraFields;
     }
 
+    #[\ReturnTypeWillChange]
     public function jsonSerialize()
     {
         return $this->getAttributes();
@@ -550,6 +551,7 @@ class TestModel4 implements \JsonSerializable
     public $field5 = 'test5';
     public $field6 = 'test6';
 
+    #[\ReturnTypeWillChange]
     public function jsonSerialize()
     {
         return [
diff --git a/tests/framework/web/ControllerTest.php b/tests/framework/web/ControllerTest.php
index 2d9b92a..4280a7b 100644
--- a/tests/framework/web/ControllerTest.php
+++ b/tests/framework/web/ControllerTest.php
@@ -80,7 +80,6 @@ class ControllerTest extends TestCase
                 ],
             ],
         ]));
-        $this->mockWebApplication(['controller' => $this->controller]);
 
         $injectionAction = new InlineAction('injection', $this->controller, 'actionNullableInjection');
         $params = [];
@@ -195,7 +194,6 @@ class ControllerTest extends TestCase
                 ],
             ],
         ]));
-        $this->mockWebApplication(['controller' => $this->controller]);
 
         $injectionAction = new InlineAction('injection', $this->controller, 'actionInjection');
         $params = ['between' => 'test', 'after' => 'another', 'before' => 'test'];