diff --git a/framework/CHANGELOG.md b/framework/CHANGELOG.md
index 0dbab372484..320f5959f49 100644
--- a/framework/CHANGELOG.md
+++ b/framework/CHANGELOG.md
@@ -25,6 +25,7 @@ Yii Framework 2 Change Log
 - Chg #20465: Remove `PHP_VERSION_ID` checks from web `Session` class (terabytesoftw)
 - Chg #20464: Remove `PHP_VERSION_ID` checks from web `Response` class (terabytesoftw)
 - Enh #20511: Allow `jQuery` usage in `View` class while maintaining backward compatibility (terabytesoftw)
+- Bug #20518: `PHP` 8.4 fixes for implicit nullability deprecation (terabytesoftw)
 
 2.0.54 under development
 ------------------------
diff --git a/tests/framework/base/ControllerTest.php b/tests/framework/base/ControllerTest.php
index c1ba6023a64..cd5ab33dfad 100644
--- a/tests/framework/base/ControllerTest.php
+++ b/tests/framework/base/ControllerTest.php
@@ -56,7 +56,7 @@ public function testRunAction(): void
     public function testCreateInlineAction(
         string $controllerClass,
         string $actionId,
-        string $expectedActionMethod = null
+        string|null $expectedActionMethod = null
     ): void {
         $this->mockApplication();
         /** @var Controller $controller */
diff --git a/tests/framework/behaviors/AttributeBehaviorTest.php b/tests/framework/behaviors/AttributeBehaviorTest.php
index ae5a32ab5fe..4ef7406dab5 100644
--- a/tests/framework/behaviors/AttributeBehaviorTest.php
+++ b/tests/framework/behaviors/AttributeBehaviorTest.php
@@ -105,7 +105,7 @@ public function testPreserveNonEmptyValues(
         string $aliasExpected,
         bool $preserveNonEmptyValues,
         string $name,
-        string $alias = null
+        string|null $alias = null
     ): void {
         $model = new ActiveRecordWithAttributeBehavior();
         $model->attributeBehavior->preserveNonEmptyValues = $preserveNonEmptyValues;
diff --git a/tests/framework/console/RequestTest.php b/tests/framework/console/RequestTest.php
index 343a7eaa281..f1bea0c9a80 100644
--- a/tests/framework/console/RequestTest.php
+++ b/tests/framework/console/RequestTest.php
@@ -185,7 +185,7 @@ public static function provider(): array
      * @param array $expected The expected result.
      * @param array|null $expectedException The expected exception.
      */
-    public function testResolve(array $params, array $expected, array $expectedException = null): void
+    public function testResolve(array $params, array $expected, array|null $expectedException = null): void
     {
         if (isset($expectedException)) {
             $this->expectException($expectedException[0]);
diff --git a/tests/framework/di/ContainerTest.php b/tests/framework/di/ContainerTest.php
index f31594034f7..8fea7be062d 100644
--- a/tests/framework/di/ContainerTest.php
+++ b/tests/framework/di/ContainerTest.php
@@ -236,7 +236,7 @@ public function testOptionalDependencies(): void
     {
         $container = new Container();
         // Test optional unresolvable dependency.
-        $closure = fn(QuxInterface $test = null) => $test;
+        $closure = fn(QuxInterface|null $test = null): QuxInterface|null => $test;
         $this->assertNull($container->invoke($closure));
     }
 
diff --git a/tests/framework/filters/AccessRuleTest.php b/tests/framework/filters/AccessRuleTest.php
index ab1e1070f75..aa5e1a098dc 100644
--- a/tests/framework/filters/AccessRuleTest.php
+++ b/tests/framework/filters/AccessRuleTest.php
@@ -44,7 +44,7 @@ protected function mockRequest(string $method = 'GET'): Request
         return $request;
     }
 
-    protected function mockUser(string $userid = null): User
+    protected function mockUser(string|null $userid = null): User
     {
         $user = new User([
             'identityClass' => UserIdentity::class,
diff --git a/tests/framework/helpers/HtmlTest.php b/tests/framework/helpers/HtmlTest.php
index 8b6201282fb..93124cbcda5 100644
--- a/tests/framework/helpers/HtmlTest.php
+++ b/tests/framework/helpers/HtmlTest.php
@@ -1652,8 +1652,12 @@ function (DynamicModel $model) {
     /**
      * @dataProvider errorSummaryDataProvider
      */
-    public function testErrorSummary(string $value, array $options, string $expectedHtml, \Closure $beforeValidate = null): void
-    {
+    public function testErrorSummary(
+        string $value,
+        array $options,
+        string $expectedHtml,
+        \Closure|null $beforeValidate = null
+    ): void {
         $model = new HtmlTestModel();
         $model->name = $value;
         if ($beforeValidate !== null) {
diff --git a/tests/framework/i18n/FormatterDateTest.php b/tests/framework/i18n/FormatterDateTest.php
index 6ee89da5fe8..63546093d50 100644
--- a/tests/framework/i18n/FormatterDateTest.php
+++ b/tests/framework/i18n/FormatterDateTest.php
@@ -554,7 +554,7 @@ public static function dateInputs()
      * @param mixed $value
      * @param mixed|null $expectedException
      */
-    public function testIntlDateInput(string|bool $expected, string $value, string $expectedException = null): void
+    public function testIntlDateInput(string|bool $expected, string $value, string|null $expectedException = null): void
     {
         $this->testDateInput($expected, $value, $expectedException);
     }
@@ -565,7 +565,7 @@ public function testIntlDateInput(string|bool $expected, string $value, string $
      * @param mixed $value
      * @param mixed|null $expectedException
      */
-    public function testDateInput(string|bool $expected, string $value, string $expectedException = null): void
+    public function testDateInput(string|bool $expected, string $value, string|null $expectedException = null): void
     {
         if ($expectedException !== null) {
             $this->expectException($expectedException);
diff --git a/tests/framework/rest/IndexActionTest.php b/tests/framework/rest/IndexActionTest.php
index 8056d851dc4..ea0313c97e1 100644
--- a/tests/framework/rest/IndexActionTest.php
+++ b/tests/framework/rest/IndexActionTest.php
@@ -75,12 +75,12 @@ public function testPrepareSearchQueryAttribute(): void
      * @param string $expectedRawSql
      */
     public function testPrepareDataProviderWithPaginationAndSorting(
-        \yii\data\Pagination|bool|array $pagination,
-        \yii\data\Sort|bool|array $sort,
-        int $expectedPaginationPageSize = null,
-        int $expectedPaginationDefaultPageSize = null,
+        Pagination|bool|array $pagination,
+        Sort|bool|array $sort,
+        int|null $expectedPaginationPageSize = null,
+        int|null $expectedPaginationDefaultPageSize = null,
         array $expectedSortOrders = [],
-        ?array $expectedSortDefaultOrder = null
+        array|null $expectedSortDefaultOrder = null
     ): void {
         Yii::$app->getRequest()->setBodyParams([
             'per-page' => 11,
diff --git a/tests/framework/web/AssetBundleTest.php b/tests/framework/web/AssetBundleTest.php
index 85d5362f142..f0ad8948ac9 100644
--- a/tests/framework/web/AssetBundleTest.php
+++ b/tests/framework/web/AssetBundleTest.php
@@ -509,8 +509,13 @@ public static function registerFileDataProvider()
      * @param string|bool $appendTimestamp
      * @param string|null $webAlias
      */
-    public function testRegisterFileAppendTimestamp(string $type, string $path, bool $appendTimestamp, string $expected, string $webAlias = null): void
-    {
+    public function testRegisterFileAppendTimestamp(
+        string $type,
+        string $path,
+        bool $appendTimestamp,
+        string $expected,
+        string|null $webAlias = null,
+    ): void {
         $originalAlias = Yii::getAlias('@web');
         if ($webAlias === null) {
             $webAlias = $originalAlias;