diff --git a/src/Container/Traits/HasLocale.php b/src/Container/Traits/HasLocale.php
index bc342a3..3fddf6f 100644
--- a/src/Container/Traits/HasLocale.php
+++ b/src/Container/Traits/HasLocale.php
@@ -7,16 +7,16 @@ trait HasLocale
     /**
      * The current locale format (BCP 47 Code).
      *
-     * @var string
+     * @var ?string
      */
-    protected string|null $locale;
+    protected ?string $locale;
 
     /**
      * Get the current locale.
      *
-     * @return string|null
+     * @return ?string
      */
-    public function getLocale(): string|null
+    public function getLocale(): ?string
     {
         return $this->locale ?? null;
     }
@@ -24,11 +24,11 @@ public function getLocale(): string|null
     /**
      * Change the locale.
      *
-     * @param string|null $locale
+     * @param ?string $locale
      *
      * @return self
      */
-    public function locale(string|null $locale): self
+    public function locale(?string $locale): self
     {
         $this->locale = $locale;
 
diff --git a/src/Extensions/FinancialExtension.php b/src/Extensions/FinancialExtension.php
index 56a86d7..7e21630 100644
--- a/src/Extensions/FinancialExtension.php
+++ b/src/Extensions/FinancialExtension.php
@@ -10,12 +10,12 @@ class FinancialExtension extends Extension
     use HasLocale;
 
     /**
-     * @param string|null $countryCode
-     * @param string|null $format      [{d} => digit, {l} => letter, {a} => any]
+     * @param ?string $countryCode
+     * @param ?string $format      [{d} => digit, {l} => letter, {a} => any]
      *
      * @return string
      */
-    public function iban(string $countryCode = null, string $format = null): string
+    public function iban(?string $countryCode = null, ?string $format = null): string
     {
         if ($format === null) {
             $format = str_repeat('{d}', 24);
diff --git a/src/Extensions/PersonExtension.php b/src/Extensions/PersonExtension.php
index 8b156b3..6a465d8 100644
--- a/src/Extensions/PersonExtension.php
+++ b/src/Extensions/PersonExtension.php
@@ -66,12 +66,12 @@ class PersonExtension extends Extension
         'Professor',
     ];
 
-    public function name(string|null $gender = null): string
+    public function name(?string $gender = null): string
     {
         return sprintf('%s %s', $this->firstName($gender), $this->lastName());
     }
 
-    public function firstName(string|null $gender = null): string
+    public function firstName(?string $gender = null): string
     {
         if ($gender === static::GENDER_MALE) {
             return $this->pickArrayRandomElement($this->firstNameMale);
@@ -89,7 +89,7 @@ public function lastName(): string
         return $this->pickArrayRandomElement($this->lastName);
     }
 
-    public function title($gender = null)
+    public function title(?string $gender = null)
     {
         if ($gender === static::GENDER_MALE) {
             return $this->pickArrayRandomElement($this->titleMale);
diff --git a/src/Extensions/Traits/HasLocale.php b/src/Extensions/Traits/HasLocale.php
index 534ca49..a5c2349 100644
--- a/src/Extensions/Traits/HasLocale.php
+++ b/src/Extensions/Traits/HasLocale.php
@@ -7,9 +7,9 @@ trait HasLocale
     /**
      * The extension locale (BCP 47 Code).
      *
-     * @return string | null
+     * @return ?string
      */
-    public function getLocale(): string|null
+    public function getLocale(): ?string
     {
         return null;
     }
diff --git a/src/Faker.php b/src/Faker.php
index 8302ab2..240dd07 100644
--- a/src/Faker.php
+++ b/src/Faker.php
@@ -12,11 +12,11 @@ class Faker
     /**
      * The current locale format (BCP 47 Code).
      *
-     * @var string|null
+     * @var ?string
      */
-    protected string|null $locale;
+    protected ?string $locale;
 
-    public function __construct(string|null $locale = null)
+    public function __construct(?string $locale = null)
     {
         $this->locale = $locale;
     }
diff --git a/src/Manifests/ContainerMixinManifest.php b/src/Manifests/ContainerMixinManifest.php
index f490fcc..965f8c1 100644
--- a/src/Manifests/ContainerMixinManifest.php
+++ b/src/Manifests/ContainerMixinManifest.php
@@ -9,6 +9,7 @@
 use phpDocumentor\Reflection\TypeResolver;
 use phpDocumentor\Reflection\Types\Intersection;
 use phpDocumentor\Reflection\Types\Mixed_;
+use phpDocumentor\Reflection\Types\Nullable;
 
 class ContainerMixinManifest
 {
@@ -36,10 +37,10 @@ class ContainerMixinManifest
     /**
      * Create a new package manifest instance.
      *
-     * @param string      $basePath
-     * @param string|null $containerMixinPath
+     * @param string  $basePath
+     * @param ?string $containerMixinPath
      */
-    public function __construct(string $basePath, string $containerMixinPath = null)
+    public function __construct(string $basePath, ?string $containerMixinPath = null)
     {
         $this->basePath = $basePath;
         $this->vendorPath = $basePath.'/vendor';
@@ -104,6 +105,10 @@ public function build(array $extensionMethods, array $extensions)
                     } else {
                         $type = $typeResolver->resolve($type->getName());
                     }
+
+                    if ($parameter->allowsNull()) {
+                        $type = new Nullable($type);
+                    }
                 }
 
                 $parameters[] = new DocBlock\Tags\MethodParameter(
diff --git a/src/Manifests/PackageManifest.php b/src/Manifests/PackageManifest.php
index 97870e4..53e964b 100644
--- a/src/Manifests/PackageManifest.php
+++ b/src/Manifests/PackageManifest.php
@@ -9,9 +9,9 @@ class PackageManifest
     /**
      * The manifest path.
      *
-     * @var string|null
+     * @var ?string
      */
-    public string|null $manifestPath;
+    public ?string $manifestPath;
 
     /**
      * The base path.
diff --git a/tests/Support/Extensions/EnEnExtensionTest.php b/tests/Support/Extensions/EnEnExtensionTest.php
index ca54850..ab131c0 100644
--- a/tests/Support/Extensions/EnEnExtensionTest.php
+++ b/tests/Support/Extensions/EnEnExtensionTest.php
@@ -14,7 +14,7 @@ public function getName(): string
         return 'locale-extension-test';
     }
 
-    public function getLocale(): string|null
+    public function getLocale(): ?string
     {
         return 'en_EN';
     }
diff --git a/tests/Support/Extensions/EnUsExtensionTest.php b/tests/Support/Extensions/EnUsExtensionTest.php
index 0dc1dce..c75ed0e 100644
--- a/tests/Support/Extensions/EnUsExtensionTest.php
+++ b/tests/Support/Extensions/EnUsExtensionTest.php
@@ -14,7 +14,7 @@ public function getName(): string
         return 'locale-extension-test';
     }
 
-    public function getLocale(): string|null
+    public function getLocale(): ?string
     {
         return 'en_US';
     }
diff --git a/tests/Support/Extensions/FrFrExtensionTest.php b/tests/Support/Extensions/FrFrExtensionTest.php
index 2c897cf..1e06584 100644
--- a/tests/Support/Extensions/FrFrExtensionTest.php
+++ b/tests/Support/Extensions/FrFrExtensionTest.php
@@ -14,7 +14,7 @@ public function getName(): string
         return 'locale-extension-test';
     }
 
-    public function getLocale(): string|null
+    public function getLocale(): ?string
     {
         return 'fr_FR';
     }
diff --git a/tests/Support/Extensions/MixinTestExtension.php b/tests/Support/Extensions/MixinTestExtension.php
index 78dea26..aa18289 100644
--- a/tests/Support/Extensions/MixinTestExtension.php
+++ b/tests/Support/Extensions/MixinTestExtension.php
@@ -26,4 +26,9 @@ public function withStringReturnType(): string
     {
         return 'string';
     }
+
+    public function withNullableParameter(?string $one = 'default value'): string
+    {
+        return 'string';
+    }
 }
diff --git a/tests/Unit/ContainerMixinManifestTest.php b/tests/Unit/ContainerMixinManifestTest.php
index c7abda1..e281ec1 100644
--- a/tests/Unit/ContainerMixinManifestTest.php
+++ b/tests/Unit/ContainerMixinManifestTest.php
@@ -53,6 +53,11 @@ public function testContainerMixinBuild()
             $containerMixinContent
         );
 
+        $this->assertStringContainsString(
+            '@method string withNullableParameter(?string $one)',
+            $containerMixinContent
+        );
+
         unlink('/tmp/ContainerMixin.php');
     }