diff --git a/CHANGELOG.md b/CHANGELOG.md
index f2de15d..2808adb 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,10 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## 0.4.2
+### Fixed
+- PHP 8.4 deprecation notices: the optional parameters of `getBool()`, `getFloat()`, `getInt()`, `getString()` and of the exception constructors are declared as explicit nullable types
+
 ## 0.4.1
 ### Fixed
 - Suppress Symfony deprecations
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index 015244f..04e9bf8 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -5,6 +5,7 @@
         backupStaticAttributes="false"
         colors="true"
         convertErrorsToExceptions="true"
+        convertDeprecationsToExceptions="true"
         convertNoticesToExceptions="true"
         convertWarningsToExceptions="true"
         processIsolation="false"
diff --git a/src/Exception/InvalidItemException.php b/src/Exception/InvalidItemException.php
index 329ace1..227ecba 100644
--- a/src/Exception/InvalidItemException.php
+++ b/src/Exception/InvalidItemException.php
@@ -3,11 +3,13 @@
 
 namespace Paysera\Component\ObjectWrapper\Exception;
 
-class InvalidItemException extends \Exception
+use Exception;
+
+class InvalidItemException extends Exception
 {
     private $key;
 
-    public function __construct(string $key, string $message = null, \Exception $previous = null)
+    public function __construct(string $key, ?string $message = null, ?Exception $previous = null)
     {
         parent::__construct($message ?? sprintf('Invalid key "%s"', $key), 0, $previous);
         $this->key = $key;
diff --git a/src/Exception/InvalidItemTypeException.php b/src/Exception/InvalidItemTypeException.php
index 043c8e1..16d4cb5 100644
--- a/src/Exception/InvalidItemTypeException.php
+++ b/src/Exception/InvalidItemTypeException.php
@@ -3,12 +3,14 @@
 
 namespace Paysera\Component\ObjectWrapper\Exception;
 
+use Exception;
+
 class InvalidItemTypeException extends InvalidItemException
 {
     private $expectedType;
     private $givenType;
 
-    public function __construct(string $expectedType, string $givenType, string $key, \Exception $previous = null)
+    public function __construct(string $expectedType, string $givenType, string $key, ?Exception $previous = null)
     {
         parent::__construct(
             $key,
diff --git a/src/Exception/MissingItemException.php b/src/Exception/MissingItemException.php
index 4874905..914805a 100644
--- a/src/Exception/MissingItemException.php
+++ b/src/Exception/MissingItemException.php
@@ -3,9 +3,11 @@
 
 namespace Paysera\Component\ObjectWrapper\Exception;
 
+use Exception;
+
 class MissingItemException extends InvalidItemException
 {
-    public function __construct(string $key, \Exception $previous = null)
+    public function __construct(string $key, ?Exception $previous = null)
     {
         parent::__construct($key, sprintf('Missing required key "%s"', $key), $previous);
     }
diff --git a/src/ObjectWrapper.php b/src/ObjectWrapper.php
index 98465ad..ae8fa13 100644
--- a/src/ObjectWrapper.php
+++ b/src/ObjectWrapper.php
@@ -103,7 +103,7 @@ public function getRequiredBool(string $key): bool
      * @param bool|null $default
      * @return bool|null
      */
-    public function getBool(string $key, bool $default = null)
+    public function getBool(string $key, ?bool $default = null)
     {
         return $this->getOfType($key, 'boolean', $default);
     }
@@ -118,7 +118,7 @@ public function getRequiredFloat(string $key): float
      * @param float|null $default
      * @return float|null
      */
-    public function getFloat(string $key, float $default = null)
+    public function getFloat(string $key, ?float $default = null)
     {
         return $this->getOfType($key, 'float', $default);
     }
@@ -133,7 +133,7 @@ public function getRequiredInt(string $key): int
      * @param int|null $default
      * @return int|null
      */
-    public function getInt(string $key, int $default = null)
+    public function getInt(string $key, ?int $default = null)
     {
         return $this->getOfType($key, 'integer', $default);
     }
@@ -162,7 +162,7 @@ public function getRequiredString(string $key): string
      * @param string|null $default
      * @return string|null
      */
-    public function getString(string $key, string $default = null)
+    public function getString(string $key, ?string $default = null)
     {
         return $this->getOfType($key, 'string', $default);
     }
diff --git a/tests/Exception/InvalidItemExceptionTest.php b/tests/Exception/InvalidItemExceptionTest.php
new file mode 100644
index 0000000..67a60cb
--- /dev/null
+++ b/tests/Exception/InvalidItemExceptionTest.php
@@ -0,0 +1,118 @@
+<?php
+declare(strict_types=1);
+
+namespace Paysera\Component\ObjectWrapper\Tests\Exception;
+
+use Exception;
+use Paysera\Component\ObjectWrapper\Exception\InvalidItemException;
+use Paysera\Component\ObjectWrapper\Exception\InvalidItemTypeException;
+use Paysera\Component\ObjectWrapper\Exception\MissingItemException;
+use PHPUnit\Framework\TestCase;
+
+class InvalidItemExceptionTest extends TestCase
+{
+    /**
+     * @dataProvider exceptionProvider
+     * @param array<string, mixed> $expected
+     */
+    public function testExceptionDescribesTheItem(callable $createException, array $expected): void
+    {
+        $exception = $createException();
+
+        $this->assertSame($expected, [
+            'class' => get_class($exception),
+            'message' => $exception->getMessage(),
+            'key' => $exception->getKey(),
+            'expectedType' => $exception instanceof InvalidItemTypeException ? $exception->getExpectedType() : null,
+            'givenType' => $exception instanceof InvalidItemTypeException ? $exception->getGivenType() : null,
+            'previous' => $exception->getPrevious(),
+        ]);
+    }
+
+    /**
+     * @return array<string, array{callable, array<string, mixed>}>
+     */
+    public static function exceptionProvider(): array
+    {
+        $previous = new Exception('x');
+
+        return [
+            'invalid item with null message and previous' => [
+                static function () {
+                    return new InvalidItemException('a.b', null, null);
+                },
+                self::expected(InvalidItemException::class, 'Invalid key "a.b"', 'a.b'),
+            ],
+            'invalid item type with a null previous exception' => [
+                static function () {
+                    return new InvalidItemTypeException('string', 'integer', 'a.b', null);
+                },
+                self::expected(
+                    InvalidItemTypeException::class,
+                    'Expected string but got integer for key "a.b"',
+                    'a.b',
+                    'string',
+                    'integer'
+                ),
+            ],
+            'missing item with a null previous exception' => [
+                static function () {
+                    return new MissingItemException('a.b', null);
+                },
+                self::expected(MissingItemException::class, 'Missing required key "a.b"', 'a.b'),
+            ],
+            'invalid item with a custom message' => [
+                static function () {
+                    return new InvalidItemException('a.b', 'Custom message');
+                },
+                self::expected(InvalidItemException::class, 'Custom message', 'a.b'),
+            ],
+            'invalid item with a previous exception' => [
+                static function () use ($previous) {
+                    return new InvalidItemException('a.b', null, $previous);
+                },
+                self::expected(InvalidItemException::class, 'Invalid key "a.b"', 'a.b', null, null, $previous),
+            ],
+            'invalid item type with a previous exception' => [
+                static function () use ($previous) {
+                    return new InvalidItemTypeException('string', 'integer', 'a.b', $previous);
+                },
+                self::expected(
+                    InvalidItemTypeException::class,
+                    'Expected string but got integer for key "a.b"',
+                    'a.b',
+                    'string',
+                    'integer',
+                    $previous
+                ),
+            ],
+            'missing item with a previous exception' => [
+                static function () use ($previous) {
+                    return new MissingItemException('a.b', $previous);
+                },
+                self::expected(MissingItemException::class, 'Missing required key "a.b"', 'a.b', null, null, $previous),
+            ],
+        ];
+    }
+
+    /**
+     * @return array<string, mixed>
+     */
+    private static function expected(
+        string $class,
+        string $message,
+        string $key,
+        ?string $expectedType = null,
+        ?string $givenType = null,
+        ?Exception $previous = null
+    ): array {
+        return [
+            'class' => $class,
+            'message' => $message,
+            'key' => $key,
+            'expectedType' => $expectedType,
+            'givenType' => $givenType,
+            'previous' => $previous,
+        ];
+    }
+}
diff --git a/tests/ObjectWrapperTest.php b/tests/ObjectWrapperTest.php
index 63c2d52..3e4d9ed 100644
--- a/tests/ObjectWrapperTest.php
+++ b/tests/ObjectWrapperTest.php
@@ -425,6 +425,30 @@ public function testGetOriginalDataAsArray()
         $this->assertDeepEquals($expectedArray, $originalData);
     }
 
+    /**
+     * @dataProvider optionalGetterProvider
+     * @param mixed $value
+     */
+    public function testOptionalGettersAcceptAnExplicitNullDefault(string $method, $value): void
+    {
+        $object = new ObjectWrapper((object)['present' => $value]);
+
+        $this->assertSame([$value, null], [$object->$method('present', null), $object->$method('absent', null)]);
+    }
+
+    /**
+     * @return array<string, array{string, mixed}>
+     */
+    public static function optionalGetterProvider(): array
+    {
+        return [
+            'getBool' => ['getBool', true],
+            'getFloat' => ['getFloat', 1.5],
+            'getInt' => ['getInt', 7],
+            'getString' => ['getString', 'text'],
+        ];
+    }
+
     private function assertDeepEquals($expectedData, $dataWithWrappers)
     {
         $this->assertEquals($expectedData, $this->unwrap($dataWithWrappers));