diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/PhpNextgenClientCodegen.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/PhpNextgenClientCodegen.java
index 43ea920fe50..5354e5c3106 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/PhpNextgenClientCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/PhpNextgenClientCodegen.java
@@ -211,15 +211,16 @@ public class PhpNextgenClientCodegen extends AbstractPhpCodegen {
             }
 
             for (CodegenParameter param : operation.allParams) {
+                String paramType;
                 if (param.isArray || param.isMap) {
-                    param.vendorExtensions.putIfAbsent("x-php-param-type", "array");
+                    paramType = "array";
                 } else {
-                    String paramType = param.dataType;
-                    if ((!param.required || param.isNullable) && !paramType.equals("mixed")) { // optional or nullable but not mixed
-                        paramType = "?" + paramType;
-                    }
-                    param.vendorExtensions.putIfAbsent("x-php-param-type", paramType);
+                    paramType = param.dataType;
                 }
+                if ((!param.required || param.isNullable) && !paramType.equals("mixed")) { // optional or nullable but not mixed
+                    paramType = "?" + paramType;
+                }
+                param.vendorExtensions.putIfAbsent("x-php-param-type", paramType);
             }
         }
 
diff --git a/modules/openapi-generator/src/main/resources/php-dt-modern/ApiClientFactory.php.mustache b/modules/openapi-generator/src/main/resources/php-dt-modern/ApiClientFactory.php.mustache
index 4e0de71da94..94ebdf78407 100644
--- a/modules/openapi-generator/src/main/resources/php-dt-modern/ApiClientFactory.php.mustache
+++ b/modules/openapi-generator/src/main/resources/php-dt-modern/ApiClientFactory.php.mustache
@@ -16,7 +16,7 @@ class ApiClientFactory implements PM\ServiceFactoryInterface
         $this->configKey = $configKey;
     }
 
-    public function __invoke(ContainerInterface $container, $requestedName, array $options = null): ApiClient
+    public function __invoke(ContainerInterface $container, $requestedName, ?array $options = null): ApiClient
     {
         $config = new OAGAC\ApiClientOptions(\array_merge($this->getServiceConfig($container), $options ?? []));
         return new ApiClient(
diff --git a/modules/openapi-generator/src/main/resources/php-dt/ApiClientFactory.php.mustache b/modules/openapi-generator/src/main/resources/php-dt/ApiClientFactory.php.mustache
index 4e0de71da94..94ebdf78407 100644
--- a/modules/openapi-generator/src/main/resources/php-dt/ApiClientFactory.php.mustache
+++ b/modules/openapi-generator/src/main/resources/php-dt/ApiClientFactory.php.mustache
@@ -16,7 +16,7 @@ class ApiClientFactory implements PM\ServiceFactoryInterface
         $this->configKey = $configKey;
     }
 
-    public function __invoke(ContainerInterface $container, $requestedName, array $options = null): ApiClient
+    public function __invoke(ContainerInterface $container, $requestedName, ?array $options = null): ApiClient
     {
         $config = new OAGAC\ApiClientOptions(\array_merge($this->getServiceConfig($container), $options ?? []));
         return new ApiClient(
diff --git a/modules/openapi-generator/src/main/resources/php-mezzio-ph-modern/Factory.php.mustache b/modules/openapi-generator/src/main/resources/php-mezzio-ph-modern/Factory.php.mustache
index c517b693604..f1244bbc7f4 100644
--- a/modules/openapi-generator/src/main/resources/php-mezzio-ph-modern/Factory.php.mustache
+++ b/modules/openapi-generator/src/main/resources/php-mezzio-ph-modern/Factory.php.mustache
@@ -21,7 +21,7 @@ use Laminas\Stratigility\MiddlewarePipe;
 
 class Factory implements FactoryInterface
 {
-    public function __invoke(ContainerInterface $container, $requestedName, array $options = null): Application
+    public function __invoke(ContainerInterface $container, $requestedName, ?array $options = null): Application
     {
         $errorMiddleware = self::getErrorMiddleware($container);
         $pipeline = new MiddlewarePipe();
diff --git a/modules/openapi-generator/src/main/resources/php-mezzio-ph/Factory.php.mustache b/modules/openapi-generator/src/main/resources/php-mezzio-ph/Factory.php.mustache
index bee7ad98a78..d8efc1a1b55 100644
--- a/modules/openapi-generator/src/main/resources/php-mezzio-ph/Factory.php.mustache
+++ b/modules/openapi-generator/src/main/resources/php-mezzio-ph/Factory.php.mustache
@@ -21,7 +21,7 @@ use Laminas\Stratigility\MiddlewarePipe;
 
 class Factory implements FactoryInterface
 {
-    public function __invoke(ContainerInterface $container, $requestedName, array $options = null): Application
+    public function __invoke(ContainerInterface $container, $requestedName, ?array $options = null): Application
     {
         $errorMiddleware = self::getErrorMiddleware($container);
         $pipeline = new MiddlewarePipe();
diff --git a/modules/openapi-generator/src/main/resources/php-nextgen/Configuration.mustache b/modules/openapi-generator/src/main/resources/php-nextgen/Configuration.mustache
index 618276f51b1..4a5119de1d8 100644
--- a/modules/openapi-generator/src/main/resources/php-nextgen/Configuration.mustache
+++ b/modules/openapi-generator/src/main/resources/php-nextgen/Configuration.mustache
@@ -498,7 +498,7 @@ class Configuration
     * @param array|null $variables    hash of variable and the corresponding value (optional)
     * @return string URL based on host settings
     */
-    public static function getHostString(array $hostSettings, int $hostIndex, array $variables = null): string
+    public static function getHostString(array $hostSettings, int $hostIndex, ?array $variables = null): string
     {
         if (null === $variables) {
             $variables = [];
diff --git a/modules/openapi-generator/src/main/resources/php-nextgen/ObjectSerializer.mustache b/modules/openapi-generator/src/main/resources/php-nextgen/ObjectSerializer.mustache
index 9c57c887441..4317aaf327a 100644
--- a/modules/openapi-generator/src/main/resources/php-nextgen/ObjectSerializer.mustache
+++ b/modules/openapi-generator/src/main/resources/php-nextgen/ObjectSerializer.mustache
@@ -56,7 +56,7 @@ class ObjectSerializer
      *
      * @return scalar|object|array|null serialized form of $data
      */
-    public static function sanitizeForSerialization(mixed $data, string $type = null, string $format = null): mixed
+    public static function sanitizeForSerialization(mixed $data, ?string $type = null, ?string $format = null): mixed
     {
         if (is_scalar($data) || null === $data) {
             return $data;
@@ -388,7 +388,7 @@ class ObjectSerializer
      *
      * @return mixed a single or an array of $class instances
      */
-    public static function deserialize(mixed $data, string $class, array $httpHeaders = null): mixed
+    public static function deserialize(mixed $data, string $class, ?array $httpHeaders = null): mixed
     {
         if (null === $data) {
             return null;
diff --git a/modules/openapi-generator/src/main/resources/php-nextgen/api.mustache b/modules/openapi-generator/src/main/resources/php-nextgen/api.mustache
index bdbe28f85c5..7d679de68df 100644
--- a/modules/openapi-generator/src/main/resources/php-nextgen/api.mustache
+++ b/modules/openapi-generator/src/main/resources/php-nextgen/api.mustache
@@ -76,9 +76,9 @@ use {{invokerPackage}}\ObjectSerializer;
      * @param int                  $hostIndex (Optional) host index to select the list of hosts if defined in the OpenAPI spec
      */
     public function __construct(
-        ClientInterface $client = null,
-        Configuration $config = null,
-        HeaderSelector $selector = null,
+        ?ClientInterface $client = null,
+        ?Configuration $config = null,
+        ?HeaderSelector $selector = null,
         int $hostIndex = 0
     ) {
         $this->client = $client ?: new Client();
diff --git a/modules/openapi-generator/src/main/resources/php-nextgen/model_generic.mustache b/modules/openapi-generator/src/main/resources/php-nextgen/model_generic.mustache
index c81f28e4190..06ff303fe6e 100644
--- a/modules/openapi-generator/src/main/resources/php-nextgen/model_generic.mustache
+++ b/modules/openapi-generator/src/main/resources/php-nextgen/model_generic.mustache
@@ -245,7 +245,7 @@ class {{classname}} {{#parentSchema}}extends {{{parent}}}{{/parentSchema}}{{^par
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         {{#discriminator}}
         // Initialize discriminator property with the model name.
diff --git a/samples/client/echo_api/php-nextgen-streaming/src/Api/AuthApi.php b/samples/client/echo_api/php-nextgen-streaming/src/Api/AuthApi.php
index b938a95968e..8f8de87fb5d 100644
--- a/samples/client/echo_api/php-nextgen-streaming/src/Api/AuthApi.php
+++ b/samples/client/echo_api/php-nextgen-streaming/src/Api/AuthApi.php
@@ -87,9 +87,9 @@ class AuthApi
      * @param int                  $hostIndex (Optional) host index to select the list of hosts if defined in the OpenAPI spec
      */
     public function __construct(
-        ClientInterface $client = null,
-        Configuration $config = null,
-        HeaderSelector $selector = null,
+        ?ClientInterface $client = null,
+        ?Configuration $config = null,
+        ?HeaderSelector $selector = null,
         int $hostIndex = 0
     ) {
         $this->client = $client ?: new Client();
diff --git a/samples/client/echo_api/php-nextgen-streaming/src/Api/BodyApi.php b/samples/client/echo_api/php-nextgen-streaming/src/Api/BodyApi.php
index 6e01f649d05..a1a66cf428e 100644
--- a/samples/client/echo_api/php-nextgen-streaming/src/Api/BodyApi.php
+++ b/samples/client/echo_api/php-nextgen-streaming/src/Api/BodyApi.php
@@ -111,9 +111,9 @@ class BodyApi
      * @param int                  $hostIndex (Optional) host index to select the list of hosts if defined in the OpenAPI spec
      */
     public function __construct(
-        ClientInterface $client = null,
-        Configuration $config = null,
-        HeaderSelector $selector = null,
+        ?ClientInterface $client = null,
+        ?Configuration $config = null,
+        ?HeaderSelector $selector = null,
         int $hostIndex = 0
     ) {
         $this->client = $client ?: new Client();
@@ -1745,7 +1745,7 @@ class BodyApi
      * @return string
      */
     public function testEchoBodyFreeFormObjectResponseString(
-        array $body = null,
+        ?array $body = null,
         string $contentType = self::contentTypes['testEchoBodyFreeFormObjectResponseString'][0]
     ): string
     {
@@ -1766,7 +1766,7 @@ class BodyApi
      * @return array of string, HTTP status code, HTTP response headers (array of strings)
      */
     public function testEchoBodyFreeFormObjectResponseStringWithHttpInfo(
-        array $body = null,
+        ?array $body = null,
         string $contentType = self::contentTypes['testEchoBodyFreeFormObjectResponseString'][0]
     ): array
     {
@@ -1893,7 +1893,7 @@ class BodyApi
      * @return PromiseInterface
      */
     public function testEchoBodyFreeFormObjectResponseStringAsync(
-        array $body = null,
+        ?array $body = null,
         string $contentType = self::contentTypes['testEchoBodyFreeFormObjectResponseString'][0]
     ): PromiseInterface
     {
@@ -1917,7 +1917,7 @@ class BodyApi
      * @return PromiseInterface
      */
     public function testEchoBodyFreeFormObjectResponseStringAsyncWithHttpInfo(
-        array $body = null,
+        ?array $body = null,
         string $contentType = self::contentTypes['testEchoBodyFreeFormObjectResponseString'][0]
     ): PromiseInterface
     {
@@ -1970,7 +1970,7 @@ class BodyApi
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testEchoBodyFreeFormObjectResponseStringRequest(
-        array $body = null,
+        ?array $body = null,
         string $contentType = self::contentTypes['testEchoBodyFreeFormObjectResponseString'][0]
     ): Request
     {
diff --git a/samples/client/echo_api/php-nextgen-streaming/src/Api/FormApi.php b/samples/client/echo_api/php-nextgen-streaming/src/Api/FormApi.php
index b0908215636..17a70483e93 100644
--- a/samples/client/echo_api/php-nextgen-streaming/src/Api/FormApi.php
+++ b/samples/client/echo_api/php-nextgen-streaming/src/Api/FormApi.php
@@ -90,9 +90,9 @@ class FormApi
      * @param int                  $hostIndex (Optional) host index to select the list of hosts if defined in the OpenAPI spec
      */
     public function __construct(
-        ClientInterface $client = null,
-        Configuration $config = null,
-        HeaderSelector $selector = null,
+        ?ClientInterface $client = null,
+        ?Configuration $config = null,
+        ?HeaderSelector $selector = null,
         int $hostIndex = 0
     ) {
         $this->client = $client ?: new Client();
diff --git a/samples/client/echo_api/php-nextgen-streaming/src/Api/HeaderApi.php b/samples/client/echo_api/php-nextgen-streaming/src/Api/HeaderApi.php
index b4bd75cc621..66b624d99f0 100644
--- a/samples/client/echo_api/php-nextgen-streaming/src/Api/HeaderApi.php
+++ b/samples/client/echo_api/php-nextgen-streaming/src/Api/HeaderApi.php
@@ -84,9 +84,9 @@ class HeaderApi
      * @param int                  $hostIndex (Optional) host index to select the list of hosts if defined in the OpenAPI spec
      */
     public function __construct(
-        ClientInterface $client = null,
-        Configuration $config = null,
-        HeaderSelector $selector = null,
+        ?ClientInterface $client = null,
+        ?Configuration $config = null,
+        ?HeaderSelector $selector = null,
         int $hostIndex = 0
     ) {
         $this->client = $client ?: new Client();
diff --git a/samples/client/echo_api/php-nextgen-streaming/src/Api/PathApi.php b/samples/client/echo_api/php-nextgen-streaming/src/Api/PathApi.php
index 577a9ce2510..b172b7e2ca5 100644
--- a/samples/client/echo_api/php-nextgen-streaming/src/Api/PathApi.php
+++ b/samples/client/echo_api/php-nextgen-streaming/src/Api/PathApi.php
@@ -84,9 +84,9 @@ class PathApi
      * @param int                  $hostIndex (Optional) host index to select the list of hosts if defined in the OpenAPI spec
      */
     public function __construct(
-        ClientInterface $client = null,
-        Configuration $config = null,
-        HeaderSelector $selector = null,
+        ?ClientInterface $client = null,
+        ?Configuration $config = null,
+        ?HeaderSelector $selector = null,
         int $hostIndex = 0
     ) {
         $this->client = $client ?: new Client();
diff --git a/samples/client/echo_api/php-nextgen-streaming/src/Api/QueryApi.php b/samples/client/echo_api/php-nextgen-streaming/src/Api/QueryApi.php
index 3a91c48f9ee..83daaa34b67 100644
--- a/samples/client/echo_api/php-nextgen-streaming/src/Api/QueryApi.php
+++ b/samples/client/echo_api/php-nextgen-streaming/src/Api/QueryApi.php
@@ -111,9 +111,9 @@ class QueryApi
      * @param int                  $hostIndex (Optional) host index to select the list of hosts if defined in the OpenAPI spec
      */
     public function __construct(
-        ClientInterface $client = null,
-        Configuration $config = null,
-        HeaderSelector $selector = null,
+        ?ClientInterface $client = null,
+        ?Configuration $config = null,
+        ?HeaderSelector $selector = null,
         int $hostIndex = 0
     ) {
         $this->client = $client ?: new Client();
@@ -1853,7 +1853,7 @@ class QueryApi
      * @return string
      */
     public function testQueryStyleFormExplodeFalseArrayInteger(
-        array $query_object = null,
+        ?array $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeFalseArrayInteger'][0]
     ): string
     {
@@ -1874,7 +1874,7 @@ class QueryApi
      * @return array of string, HTTP status code, HTTP response headers (array of strings)
      */
     public function testQueryStyleFormExplodeFalseArrayIntegerWithHttpInfo(
-        array $query_object = null,
+        ?array $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeFalseArrayInteger'][0]
     ): array
     {
@@ -2001,7 +2001,7 @@ class QueryApi
      * @return PromiseInterface
      */
     public function testQueryStyleFormExplodeFalseArrayIntegerAsync(
-        array $query_object = null,
+        ?array $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeFalseArrayInteger'][0]
     ): PromiseInterface
     {
@@ -2025,7 +2025,7 @@ class QueryApi
      * @return PromiseInterface
      */
     public function testQueryStyleFormExplodeFalseArrayIntegerAsyncWithHttpInfo(
-        array $query_object = null,
+        ?array $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeFalseArrayInteger'][0]
     ): PromiseInterface
     {
@@ -2078,7 +2078,7 @@ class QueryApi
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testQueryStyleFormExplodeFalseArrayIntegerRequest(
-        array $query_object = null,
+        ?array $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeFalseArrayInteger'][0]
     ): Request
     {
@@ -2171,7 +2171,7 @@ class QueryApi
      * @return string
      */
     public function testQueryStyleFormExplodeFalseArrayString(
-        array $query_object = null,
+        ?array $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeFalseArrayString'][0]
     ): string
     {
@@ -2192,7 +2192,7 @@ class QueryApi
      * @return array of string, HTTP status code, HTTP response headers (array of strings)
      */
     public function testQueryStyleFormExplodeFalseArrayStringWithHttpInfo(
-        array $query_object = null,
+        ?array $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeFalseArrayString'][0]
     ): array
     {
@@ -2319,7 +2319,7 @@ class QueryApi
      * @return PromiseInterface
      */
     public function testQueryStyleFormExplodeFalseArrayStringAsync(
-        array $query_object = null,
+        ?array $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeFalseArrayString'][0]
     ): PromiseInterface
     {
@@ -2343,7 +2343,7 @@ class QueryApi
      * @return PromiseInterface
      */
     public function testQueryStyleFormExplodeFalseArrayStringAsyncWithHttpInfo(
-        array $query_object = null,
+        ?array $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeFalseArrayString'][0]
     ): PromiseInterface
     {
@@ -2396,7 +2396,7 @@ class QueryApi
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testQueryStyleFormExplodeFalseArrayStringRequest(
-        array $query_object = null,
+        ?array $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeFalseArrayString'][0]
     ): Request
     {
diff --git a/samples/client/echo_api/php-nextgen-streaming/src/Configuration.php b/samples/client/echo_api/php-nextgen-streaming/src/Configuration.php
index ae7b85f4813..70e55dd1818 100644
--- a/samples/client/echo_api/php-nextgen-streaming/src/Configuration.php
+++ b/samples/client/echo_api/php-nextgen-streaming/src/Configuration.php
@@ -482,7 +482,7 @@ class Configuration
     * @param array|null $variables    hash of variable and the corresponding value (optional)
     * @return string URL based on host settings
     */
-    public static function getHostString(array $hostSettings, int $hostIndex, array $variables = null): string
+    public static function getHostString(array $hostSettings, int $hostIndex, ?array $variables = null): string
     {
         if (null === $variables) {
             $variables = [];
diff --git a/samples/client/echo_api/php-nextgen-streaming/src/Model/Bird.php b/samples/client/echo_api/php-nextgen-streaming/src/Model/Bird.php
index b394383b5f4..0db8bf2ea6e 100644
--- a/samples/client/echo_api/php-nextgen-streaming/src/Model/Bird.php
+++ b/samples/client/echo_api/php-nextgen-streaming/src/Model/Bird.php
@@ -247,7 +247,7 @@ class Bird implements ModelInterface, ArrayAccess, JsonSerializable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('size', $data ?? [], null);
         $this->setIfExists('color', $data ?? [], null);
diff --git a/samples/client/echo_api/php-nextgen-streaming/src/Model/Category.php b/samples/client/echo_api/php-nextgen-streaming/src/Model/Category.php
index 3ff8c72b4d7..64c091555c7 100644
--- a/samples/client/echo_api/php-nextgen-streaming/src/Model/Category.php
+++ b/samples/client/echo_api/php-nextgen-streaming/src/Model/Category.php
@@ -247,7 +247,7 @@ class Category implements ModelInterface, ArrayAccess, JsonSerializable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('id', $data ?? [], null);
         $this->setIfExists('name', $data ?? [], null);
diff --git a/samples/client/echo_api/php-nextgen-streaming/src/Model/DataQuery.php b/samples/client/echo_api/php-nextgen-streaming/src/Model/DataQuery.php
index a9b94be6126..a2b931e5aed 100644
--- a/samples/client/echo_api/php-nextgen-streaming/src/Model/DataQuery.php
+++ b/samples/client/echo_api/php-nextgen-streaming/src/Model/DataQuery.php
@@ -241,7 +241,7 @@ class DataQuery extends Query
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         parent::__construct($data);
 
diff --git a/samples/client/echo_api/php-nextgen-streaming/src/Model/DefaultValue.php b/samples/client/echo_api/php-nextgen-streaming/src/Model/DefaultValue.php
index c05b7828c43..ffba2c39486 100644
--- a/samples/client/echo_api/php-nextgen-streaming/src/Model/DefaultValue.php
+++ b/samples/client/echo_api/php-nextgen-streaming/src/Model/DefaultValue.php
@@ -301,7 +301,7 @@ class DefaultValue implements ModelInterface, ArrayAccess, JsonSerializable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('array_string_enum_ref_default', $data ?? [], [["success","failure"]]);
         $this->setIfExists('array_string_enum_default', $data ?? [], [["success","failure"]]);
diff --git a/samples/client/echo_api/php-nextgen-streaming/src/Model/NumberPropertiesOnly.php b/samples/client/echo_api/php-nextgen-streaming/src/Model/NumberPropertiesOnly.php
index e9659149988..d73348caae8 100644
--- a/samples/client/echo_api/php-nextgen-streaming/src/Model/NumberPropertiesOnly.php
+++ b/samples/client/echo_api/php-nextgen-streaming/src/Model/NumberPropertiesOnly.php
@@ -253,7 +253,7 @@ class NumberPropertiesOnly implements ModelInterface, ArrayAccess, JsonSerializa
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('number', $data ?? [], null);
         $this->setIfExists('float', $data ?? [], null);
diff --git a/samples/client/echo_api/php-nextgen-streaming/src/Model/Pet.php b/samples/client/echo_api/php-nextgen-streaming/src/Model/Pet.php
index d3bcfc92864..8ff05ebc0a8 100644
--- a/samples/client/echo_api/php-nextgen-streaming/src/Model/Pet.php
+++ b/samples/client/echo_api/php-nextgen-streaming/src/Model/Pet.php
@@ -288,7 +288,7 @@ class Pet implements ModelInterface, ArrayAccess, JsonSerializable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('id', $data ?? [], null);
         $this->setIfExists('name', $data ?? [], null);
diff --git a/samples/client/echo_api/php-nextgen-streaming/src/Model/Query.php b/samples/client/echo_api/php-nextgen-streaming/src/Model/Query.php
index 8bda6431741..49b71d7b1ee 100644
--- a/samples/client/echo_api/php-nextgen-streaming/src/Model/Query.php
+++ b/samples/client/echo_api/php-nextgen-streaming/src/Model/Query.php
@@ -264,7 +264,7 @@ class Query implements ModelInterface, ArrayAccess, JsonSerializable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('id', $data ?? [], null);
         $this->setIfExists('outcomes', $data ?? [], [["SUCCESS","FAILURE"]]);
diff --git a/samples/client/echo_api/php-nextgen-streaming/src/Model/Tag.php b/samples/client/echo_api/php-nextgen-streaming/src/Model/Tag.php
index 94ab33a8a11..486b73365c3 100644
--- a/samples/client/echo_api/php-nextgen-streaming/src/Model/Tag.php
+++ b/samples/client/echo_api/php-nextgen-streaming/src/Model/Tag.php
@@ -247,7 +247,7 @@ class Tag implements ModelInterface, ArrayAccess, JsonSerializable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('id', $data ?? [], null);
         $this->setIfExists('name', $data ?? [], null);
diff --git a/samples/client/echo_api/php-nextgen-streaming/src/Model/TestFormObjectMultipartRequestMarker.php b/samples/client/echo_api/php-nextgen-streaming/src/Model/TestFormObjectMultipartRequestMarker.php
index f3f21a5956e..4b8b2443a91 100644
--- a/samples/client/echo_api/php-nextgen-streaming/src/Model/TestFormObjectMultipartRequestMarker.php
+++ b/samples/client/echo_api/php-nextgen-streaming/src/Model/TestFormObjectMultipartRequestMarker.php
@@ -241,7 +241,7 @@ class TestFormObjectMultipartRequestMarker implements ModelInterface, ArrayAcces
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('name', $data ?? [], null);
     }
diff --git a/samples/client/echo_api/php-nextgen-streaming/src/Model/TestQueryStyleDeepObjectExplodeTrueObjectAllOfQueryObjectParameter.php b/samples/client/echo_api/php-nextgen-streaming/src/Model/TestQueryStyleDeepObjectExplodeTrueObjectAllOfQueryObjectParameter.php
index b8011c70a18..7fc82f05c2c 100644
--- a/samples/client/echo_api/php-nextgen-streaming/src/Model/TestQueryStyleDeepObjectExplodeTrueObjectAllOfQueryObjectParameter.php
+++ b/samples/client/echo_api/php-nextgen-streaming/src/Model/TestQueryStyleDeepObjectExplodeTrueObjectAllOfQueryObjectParameter.php
@@ -259,7 +259,7 @@ class TestQueryStyleDeepObjectExplodeTrueObjectAllOfQueryObjectParameter impleme
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('size', $data ?? [], null);
         $this->setIfExists('color', $data ?? [], null);
diff --git a/samples/client/echo_api/php-nextgen-streaming/src/Model/TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter.php b/samples/client/echo_api/php-nextgen-streaming/src/Model/TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter.php
index 7c73ed1344c..899393dca7b 100644
--- a/samples/client/echo_api/php-nextgen-streaming/src/Model/TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter.php
+++ b/samples/client/echo_api/php-nextgen-streaming/src/Model/TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter.php
@@ -241,7 +241,7 @@ class TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter implements Mo
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('values', $data ?? [], null);
     }
diff --git a/samples/client/echo_api/php-nextgen-streaming/src/ObjectSerializer.php b/samples/client/echo_api/php-nextgen-streaming/src/ObjectSerializer.php
index 1a1e0c5b832..c76724d4587 100644
--- a/samples/client/echo_api/php-nextgen-streaming/src/ObjectSerializer.php
+++ b/samples/client/echo_api/php-nextgen-streaming/src/ObjectSerializer.php
@@ -66,7 +66,7 @@ class ObjectSerializer
      *
      * @return scalar|object|array|null serialized form of $data
      */
-    public static function sanitizeForSerialization(mixed $data, string $type = null, string $format = null): mixed
+    public static function sanitizeForSerialization(mixed $data, ?string $type = null, ?string $format = null): mixed
     {
         if (is_scalar($data) || null === $data) {
             return $data;
@@ -398,7 +398,7 @@ class ObjectSerializer
      *
      * @return mixed a single or an array of $class instances
      */
-    public static function deserialize(mixed $data, string $class, array $httpHeaders = null): mixed
+    public static function deserialize(mixed $data, string $class, ?array $httpHeaders = null): mixed
     {
         if (null === $data) {
             return null;
diff --git a/samples/client/echo_api/php-nextgen/src/Api/AuthApi.php b/samples/client/echo_api/php-nextgen/src/Api/AuthApi.php
index b938a95968e..8f8de87fb5d 100644
--- a/samples/client/echo_api/php-nextgen/src/Api/AuthApi.php
+++ b/samples/client/echo_api/php-nextgen/src/Api/AuthApi.php
@@ -87,9 +87,9 @@ class AuthApi
      * @param int                  $hostIndex (Optional) host index to select the list of hosts if defined in the OpenAPI spec
      */
     public function __construct(
-        ClientInterface $client = null,
-        Configuration $config = null,
-        HeaderSelector $selector = null,
+        ?ClientInterface $client = null,
+        ?Configuration $config = null,
+        ?HeaderSelector $selector = null,
         int $hostIndex = 0
     ) {
         $this->client = $client ?: new Client();
diff --git a/samples/client/echo_api/php-nextgen/src/Api/BodyApi.php b/samples/client/echo_api/php-nextgen/src/Api/BodyApi.php
index 71f4be9f015..cbee906dcda 100644
--- a/samples/client/echo_api/php-nextgen/src/Api/BodyApi.php
+++ b/samples/client/echo_api/php-nextgen/src/Api/BodyApi.php
@@ -111,9 +111,9 @@ class BodyApi
      * @param int                  $hostIndex (Optional) host index to select the list of hosts if defined in the OpenAPI spec
      */
     public function __construct(
-        ClientInterface $client = null,
-        Configuration $config = null,
-        HeaderSelector $selector = null,
+        ?ClientInterface $client = null,
+        ?Configuration $config = null,
+        ?HeaderSelector $selector = null,
         int $hostIndex = 0
     ) {
         $this->client = $client ?: new Client();
@@ -1745,7 +1745,7 @@ class BodyApi
      * @return string
      */
     public function testEchoBodyFreeFormObjectResponseString(
-        array $body = null,
+        ?array $body = null,
         string $contentType = self::contentTypes['testEchoBodyFreeFormObjectResponseString'][0]
     ): string
     {
@@ -1766,7 +1766,7 @@ class BodyApi
      * @return array of string, HTTP status code, HTTP response headers (array of strings)
      */
     public function testEchoBodyFreeFormObjectResponseStringWithHttpInfo(
-        array $body = null,
+        ?array $body = null,
         string $contentType = self::contentTypes['testEchoBodyFreeFormObjectResponseString'][0]
     ): array
     {
@@ -1893,7 +1893,7 @@ class BodyApi
      * @return PromiseInterface
      */
     public function testEchoBodyFreeFormObjectResponseStringAsync(
-        array $body = null,
+        ?array $body = null,
         string $contentType = self::contentTypes['testEchoBodyFreeFormObjectResponseString'][0]
     ): PromiseInterface
     {
@@ -1917,7 +1917,7 @@ class BodyApi
      * @return PromiseInterface
      */
     public function testEchoBodyFreeFormObjectResponseStringAsyncWithHttpInfo(
-        array $body = null,
+        ?array $body = null,
         string $contentType = self::contentTypes['testEchoBodyFreeFormObjectResponseString'][0]
     ): PromiseInterface
     {
@@ -1970,7 +1970,7 @@ class BodyApi
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testEchoBodyFreeFormObjectResponseStringRequest(
-        array $body = null,
+        ?array $body = null,
         string $contentType = self::contentTypes['testEchoBodyFreeFormObjectResponseString'][0]
     ): Request
     {
diff --git a/samples/client/echo_api/php-nextgen/src/Api/FormApi.php b/samples/client/echo_api/php-nextgen/src/Api/FormApi.php
index b0908215636..17a70483e93 100644
--- a/samples/client/echo_api/php-nextgen/src/Api/FormApi.php
+++ b/samples/client/echo_api/php-nextgen/src/Api/FormApi.php
@@ -90,9 +90,9 @@ class FormApi
      * @param int                  $hostIndex (Optional) host index to select the list of hosts if defined in the OpenAPI spec
      */
     public function __construct(
-        ClientInterface $client = null,
-        Configuration $config = null,
-        HeaderSelector $selector = null,
+        ?ClientInterface $client = null,
+        ?Configuration $config = null,
+        ?HeaderSelector $selector = null,
         int $hostIndex = 0
     ) {
         $this->client = $client ?: new Client();
diff --git a/samples/client/echo_api/php-nextgen/src/Api/HeaderApi.php b/samples/client/echo_api/php-nextgen/src/Api/HeaderApi.php
index b4bd75cc621..66b624d99f0 100644
--- a/samples/client/echo_api/php-nextgen/src/Api/HeaderApi.php
+++ b/samples/client/echo_api/php-nextgen/src/Api/HeaderApi.php
@@ -84,9 +84,9 @@ class HeaderApi
      * @param int                  $hostIndex (Optional) host index to select the list of hosts if defined in the OpenAPI spec
      */
     public function __construct(
-        ClientInterface $client = null,
-        Configuration $config = null,
-        HeaderSelector $selector = null,
+        ?ClientInterface $client = null,
+        ?Configuration $config = null,
+        ?HeaderSelector $selector = null,
         int $hostIndex = 0
     ) {
         $this->client = $client ?: new Client();
diff --git a/samples/client/echo_api/php-nextgen/src/Api/PathApi.php b/samples/client/echo_api/php-nextgen/src/Api/PathApi.php
index 577a9ce2510..b172b7e2ca5 100644
--- a/samples/client/echo_api/php-nextgen/src/Api/PathApi.php
+++ b/samples/client/echo_api/php-nextgen/src/Api/PathApi.php
@@ -84,9 +84,9 @@ class PathApi
      * @param int                  $hostIndex (Optional) host index to select the list of hosts if defined in the OpenAPI spec
      */
     public function __construct(
-        ClientInterface $client = null,
-        Configuration $config = null,
-        HeaderSelector $selector = null,
+        ?ClientInterface $client = null,
+        ?Configuration $config = null,
+        ?HeaderSelector $selector = null,
         int $hostIndex = 0
     ) {
         $this->client = $client ?: new Client();
diff --git a/samples/client/echo_api/php-nextgen/src/Api/QueryApi.php b/samples/client/echo_api/php-nextgen/src/Api/QueryApi.php
index 3a91c48f9ee..83daaa34b67 100644
--- a/samples/client/echo_api/php-nextgen/src/Api/QueryApi.php
+++ b/samples/client/echo_api/php-nextgen/src/Api/QueryApi.php
@@ -111,9 +111,9 @@ class QueryApi
      * @param int                  $hostIndex (Optional) host index to select the list of hosts if defined in the OpenAPI spec
      */
     public function __construct(
-        ClientInterface $client = null,
-        Configuration $config = null,
-        HeaderSelector $selector = null,
+        ?ClientInterface $client = null,
+        ?Configuration $config = null,
+        ?HeaderSelector $selector = null,
         int $hostIndex = 0
     ) {
         $this->client = $client ?: new Client();
@@ -1853,7 +1853,7 @@ class QueryApi
      * @return string
      */
     public function testQueryStyleFormExplodeFalseArrayInteger(
-        array $query_object = null,
+        ?array $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeFalseArrayInteger'][0]
     ): string
     {
@@ -1874,7 +1874,7 @@ class QueryApi
      * @return array of string, HTTP status code, HTTP response headers (array of strings)
      */
     public function testQueryStyleFormExplodeFalseArrayIntegerWithHttpInfo(
-        array $query_object = null,
+        ?array $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeFalseArrayInteger'][0]
     ): array
     {
@@ -2001,7 +2001,7 @@ class QueryApi
      * @return PromiseInterface
      */
     public function testQueryStyleFormExplodeFalseArrayIntegerAsync(
-        array $query_object = null,
+        ?array $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeFalseArrayInteger'][0]
     ): PromiseInterface
     {
@@ -2025,7 +2025,7 @@ class QueryApi
      * @return PromiseInterface
      */
     public function testQueryStyleFormExplodeFalseArrayIntegerAsyncWithHttpInfo(
-        array $query_object = null,
+        ?array $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeFalseArrayInteger'][0]
     ): PromiseInterface
     {
@@ -2078,7 +2078,7 @@ class QueryApi
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testQueryStyleFormExplodeFalseArrayIntegerRequest(
-        array $query_object = null,
+        ?array $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeFalseArrayInteger'][0]
     ): Request
     {
@@ -2171,7 +2171,7 @@ class QueryApi
      * @return string
      */
     public function testQueryStyleFormExplodeFalseArrayString(
-        array $query_object = null,
+        ?array $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeFalseArrayString'][0]
     ): string
     {
@@ -2192,7 +2192,7 @@ class QueryApi
      * @return array of string, HTTP status code, HTTP response headers (array of strings)
      */
     public function testQueryStyleFormExplodeFalseArrayStringWithHttpInfo(
-        array $query_object = null,
+        ?array $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeFalseArrayString'][0]
     ): array
     {
@@ -2319,7 +2319,7 @@ class QueryApi
      * @return PromiseInterface
      */
     public function testQueryStyleFormExplodeFalseArrayStringAsync(
-        array $query_object = null,
+        ?array $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeFalseArrayString'][0]
     ): PromiseInterface
     {
@@ -2343,7 +2343,7 @@ class QueryApi
      * @return PromiseInterface
      */
     public function testQueryStyleFormExplodeFalseArrayStringAsyncWithHttpInfo(
-        array $query_object = null,
+        ?array $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeFalseArrayString'][0]
     ): PromiseInterface
     {
@@ -2396,7 +2396,7 @@ class QueryApi
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testQueryStyleFormExplodeFalseArrayStringRequest(
-        array $query_object = null,
+        ?array $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeFalseArrayString'][0]
     ): Request
     {
diff --git a/samples/client/echo_api/php-nextgen/src/Configuration.php b/samples/client/echo_api/php-nextgen/src/Configuration.php
index ae7b85f4813..70e55dd1818 100644
--- a/samples/client/echo_api/php-nextgen/src/Configuration.php
+++ b/samples/client/echo_api/php-nextgen/src/Configuration.php
@@ -482,7 +482,7 @@ class Configuration
     * @param array|null $variables    hash of variable and the corresponding value (optional)
     * @return string URL based on host settings
     */
-    public static function getHostString(array $hostSettings, int $hostIndex, array $variables = null): string
+    public static function getHostString(array $hostSettings, int $hostIndex, ?array $variables = null): string
     {
         if (null === $variables) {
             $variables = [];
diff --git a/samples/client/echo_api/php-nextgen/src/Model/Bird.php b/samples/client/echo_api/php-nextgen/src/Model/Bird.php
index b394383b5f4..0db8bf2ea6e 100644
--- a/samples/client/echo_api/php-nextgen/src/Model/Bird.php
+++ b/samples/client/echo_api/php-nextgen/src/Model/Bird.php
@@ -247,7 +247,7 @@ class Bird implements ModelInterface, ArrayAccess, JsonSerializable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('size', $data ?? [], null);
         $this->setIfExists('color', $data ?? [], null);
diff --git a/samples/client/echo_api/php-nextgen/src/Model/Category.php b/samples/client/echo_api/php-nextgen/src/Model/Category.php
index 3ff8c72b4d7..64c091555c7 100644
--- a/samples/client/echo_api/php-nextgen/src/Model/Category.php
+++ b/samples/client/echo_api/php-nextgen/src/Model/Category.php
@@ -247,7 +247,7 @@ class Category implements ModelInterface, ArrayAccess, JsonSerializable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('id', $data ?? [], null);
         $this->setIfExists('name', $data ?? [], null);
diff --git a/samples/client/echo_api/php-nextgen/src/Model/DataQuery.php b/samples/client/echo_api/php-nextgen/src/Model/DataQuery.php
index a9b94be6126..a2b931e5aed 100644
--- a/samples/client/echo_api/php-nextgen/src/Model/DataQuery.php
+++ b/samples/client/echo_api/php-nextgen/src/Model/DataQuery.php
@@ -241,7 +241,7 @@ class DataQuery extends Query
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         parent::__construct($data);
 
diff --git a/samples/client/echo_api/php-nextgen/src/Model/DefaultValue.php b/samples/client/echo_api/php-nextgen/src/Model/DefaultValue.php
index c05b7828c43..ffba2c39486 100644
--- a/samples/client/echo_api/php-nextgen/src/Model/DefaultValue.php
+++ b/samples/client/echo_api/php-nextgen/src/Model/DefaultValue.php
@@ -301,7 +301,7 @@ class DefaultValue implements ModelInterface, ArrayAccess, JsonSerializable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('array_string_enum_ref_default', $data ?? [], [["success","failure"]]);
         $this->setIfExists('array_string_enum_default', $data ?? [], [["success","failure"]]);
diff --git a/samples/client/echo_api/php-nextgen/src/Model/NumberPropertiesOnly.php b/samples/client/echo_api/php-nextgen/src/Model/NumberPropertiesOnly.php
index e9659149988..d73348caae8 100644
--- a/samples/client/echo_api/php-nextgen/src/Model/NumberPropertiesOnly.php
+++ b/samples/client/echo_api/php-nextgen/src/Model/NumberPropertiesOnly.php
@@ -253,7 +253,7 @@ class NumberPropertiesOnly implements ModelInterface, ArrayAccess, JsonSerializa
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('number', $data ?? [], null);
         $this->setIfExists('float', $data ?? [], null);
diff --git a/samples/client/echo_api/php-nextgen/src/Model/Pet.php b/samples/client/echo_api/php-nextgen/src/Model/Pet.php
index d3bcfc92864..8ff05ebc0a8 100644
--- a/samples/client/echo_api/php-nextgen/src/Model/Pet.php
+++ b/samples/client/echo_api/php-nextgen/src/Model/Pet.php
@@ -288,7 +288,7 @@ class Pet implements ModelInterface, ArrayAccess, JsonSerializable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('id', $data ?? [], null);
         $this->setIfExists('name', $data ?? [], null);
diff --git a/samples/client/echo_api/php-nextgen/src/Model/Query.php b/samples/client/echo_api/php-nextgen/src/Model/Query.php
index 8bda6431741..49b71d7b1ee 100644
--- a/samples/client/echo_api/php-nextgen/src/Model/Query.php
+++ b/samples/client/echo_api/php-nextgen/src/Model/Query.php
@@ -264,7 +264,7 @@ class Query implements ModelInterface, ArrayAccess, JsonSerializable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('id', $data ?? [], null);
         $this->setIfExists('outcomes', $data ?? [], [["SUCCESS","FAILURE"]]);
diff --git a/samples/client/echo_api/php-nextgen/src/Model/Tag.php b/samples/client/echo_api/php-nextgen/src/Model/Tag.php
index 94ab33a8a11..486b73365c3 100644
--- a/samples/client/echo_api/php-nextgen/src/Model/Tag.php
+++ b/samples/client/echo_api/php-nextgen/src/Model/Tag.php
@@ -247,7 +247,7 @@ class Tag implements ModelInterface, ArrayAccess, JsonSerializable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('id', $data ?? [], null);
         $this->setIfExists('name', $data ?? [], null);
diff --git a/samples/client/echo_api/php-nextgen/src/Model/TestFormObjectMultipartRequestMarker.php b/samples/client/echo_api/php-nextgen/src/Model/TestFormObjectMultipartRequestMarker.php
index f3f21a5956e..4b8b2443a91 100644
--- a/samples/client/echo_api/php-nextgen/src/Model/TestFormObjectMultipartRequestMarker.php
+++ b/samples/client/echo_api/php-nextgen/src/Model/TestFormObjectMultipartRequestMarker.php
@@ -241,7 +241,7 @@ class TestFormObjectMultipartRequestMarker implements ModelInterface, ArrayAcces
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('name', $data ?? [], null);
     }
diff --git a/samples/client/echo_api/php-nextgen/src/Model/TestQueryStyleDeepObjectExplodeTrueObjectAllOfQueryObjectParameter.php b/samples/client/echo_api/php-nextgen/src/Model/TestQueryStyleDeepObjectExplodeTrueObjectAllOfQueryObjectParameter.php
index b8011c70a18..7fc82f05c2c 100644
--- a/samples/client/echo_api/php-nextgen/src/Model/TestQueryStyleDeepObjectExplodeTrueObjectAllOfQueryObjectParameter.php
+++ b/samples/client/echo_api/php-nextgen/src/Model/TestQueryStyleDeepObjectExplodeTrueObjectAllOfQueryObjectParameter.php
@@ -259,7 +259,7 @@ class TestQueryStyleDeepObjectExplodeTrueObjectAllOfQueryObjectParameter impleme
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('size', $data ?? [], null);
         $this->setIfExists('color', $data ?? [], null);
diff --git a/samples/client/echo_api/php-nextgen/src/Model/TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter.php b/samples/client/echo_api/php-nextgen/src/Model/TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter.php
index 7c73ed1344c..899393dca7b 100644
--- a/samples/client/echo_api/php-nextgen/src/Model/TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter.php
+++ b/samples/client/echo_api/php-nextgen/src/Model/TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter.php
@@ -241,7 +241,7 @@ class TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter implements Mo
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('values', $data ?? [], null);
     }
diff --git a/samples/client/echo_api/php-nextgen/src/ObjectSerializer.php b/samples/client/echo_api/php-nextgen/src/ObjectSerializer.php
index 1a1e0c5b832..c76724d4587 100644
--- a/samples/client/echo_api/php-nextgen/src/ObjectSerializer.php
+++ b/samples/client/echo_api/php-nextgen/src/ObjectSerializer.php
@@ -66,7 +66,7 @@ class ObjectSerializer
      *
      * @return scalar|object|array|null serialized form of $data
      */
-    public static function sanitizeForSerialization(mixed $data, string $type = null, string $format = null): mixed
+    public static function sanitizeForSerialization(mixed $data, ?string $type = null, ?string $format = null): mixed
     {
         if (is_scalar($data) || null === $data) {
             return $data;
@@ -398,7 +398,7 @@ class ObjectSerializer
      *
      * @return mixed a single or an array of $class instances
      */
-    public static function deserialize(mixed $data, string $class, array $httpHeaders = null): mixed
+    public static function deserialize(mixed $data, string $class, ?array $httpHeaders = null): mixed
     {
         if (null === $data) {
             return null;
diff --git a/samples/client/petstore/php-dt-modern/src/App/ApiClientFactory.php b/samples/client/petstore/php-dt-modern/src/App/ApiClientFactory.php
index 03ca27c58ee..fd5b72ba4d2 100644
--- a/samples/client/petstore/php-dt-modern/src/App/ApiClientFactory.php
+++ b/samples/client/petstore/php-dt-modern/src/App/ApiClientFactory.php
@@ -16,7 +16,7 @@ class ApiClientFactory implements PM\ServiceFactoryInterface
         $this->configKey = $configKey;
     }
 
-    public function __invoke(ContainerInterface $container, $requestedName, array $options = null): ApiClient
+    public function __invoke(ContainerInterface $container, $requestedName, ?array $options = null): ApiClient
     {
         $config = new OAGAC\ApiClientOptions(\array_merge($this->getServiceConfig($container), $options ?? []));
         return new ApiClient(
diff --git a/samples/client/petstore/php-dt/src/App/ApiClientFactory.php b/samples/client/petstore/php-dt/src/App/ApiClientFactory.php
index 03ca27c58ee..fd5b72ba4d2 100644
--- a/samples/client/petstore/php-dt/src/App/ApiClientFactory.php
+++ b/samples/client/petstore/php-dt/src/App/ApiClientFactory.php
@@ -16,7 +16,7 @@ class ApiClientFactory implements PM\ServiceFactoryInterface
         $this->configKey = $configKey;
     }
 
-    public function __invoke(ContainerInterface $container, $requestedName, array $options = null): ApiClient
+    public function __invoke(ContainerInterface $container, $requestedName, ?array $options = null): ApiClient
     {
         $config = new OAGAC\ApiClientOptions(\array_merge($this->getServiceConfig($container), $options ?? []));
         return new ApiClient(
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/AnotherFakeApi.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/AnotherFakeApi.php
index 986db424001..6e6ad0f6d52 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/AnotherFakeApi.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/AnotherFakeApi.php
@@ -83,9 +83,9 @@ class AnotherFakeApi
      * @param int                  $hostIndex (Optional) host index to select the list of hosts if defined in the OpenAPI spec
      */
     public function __construct(
-        ClientInterface $client = null,
-        Configuration $config = null,
-        HeaderSelector $selector = null,
+        ?ClientInterface $client = null,
+        ?Configuration $config = null,
+        ?HeaderSelector $selector = null,
         int $hostIndex = 0
     ) {
         $this->client = $client ?: new Client();
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/DefaultApi.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/DefaultApi.php
index fc917db4766..faf8c89f39a 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/DefaultApi.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/DefaultApi.php
@@ -83,9 +83,9 @@ class DefaultApi
      * @param int                  $hostIndex (Optional) host index to select the list of hosts if defined in the OpenAPI spec
      */
     public function __construct(
-        ClientInterface $client = null,
-        Configuration $config = null,
-        HeaderSelector $selector = null,
+        ?ClientInterface $client = null,
+        ?Configuration $config = null,
+        ?HeaderSelector $selector = null,
         int $hostIndex = 0
     ) {
         $this->client = $client ?: new Client();
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/FakeApi.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/FakeApi.php
index 31de89ed846..a19ddcfdb56 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/FakeApi.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/FakeApi.php
@@ -150,9 +150,9 @@ class FakeApi
      * @param int                  $hostIndex (Optional) host index to select the list of hosts if defined in the OpenAPI spec
      */
     public function __construct(
-        ClientInterface $client = null,
-        Configuration $config = null,
-        HeaderSelector $selector = null,
+        ?ClientInterface $client = null,
+        ?Configuration $config = null,
+        ?HeaderSelector $selector = null,
         int $hostIndex = 0
     ) {
         $this->client = $client ?: new Client();
@@ -4728,14 +4728,14 @@ class FakeApi
      * @return void
      */
     public function testEnumParameters(
-        array $enum_header_string_array = ['$'],
+        ?array $enum_header_string_array = ['$'],
         ?string $enum_header_string = '-efg',
-        array $enum_query_string_array = ['$'],
+        ?array $enum_query_string_array = ['$'],
         ?string $enum_query_string = '-efg',
         ?int $enum_query_integer = null,
         ?float $enum_query_double = null,
-        array $enum_query_model_array = null,
-        array $enum_form_string_array = ['$'],
+        ?array $enum_query_model_array = null,
+        ?array $enum_form_string_array = ['$'],
         ?string $enum_form_string = '-efg',
         string $contentType = self::contentTypes['testEnumParameters'][0]
     ): void
@@ -4764,14 +4764,14 @@ class FakeApi
      * @return array of null, HTTP status code, HTTP response headers (array of strings)
      */
     public function testEnumParametersWithHttpInfo(
-        array $enum_header_string_array = ['$'],
+        ?array $enum_header_string_array = ['$'],
         ?string $enum_header_string = '-efg',
-        array $enum_query_string_array = ['$'],
+        ?array $enum_query_string_array = ['$'],
         ?string $enum_query_string = '-efg',
         ?int $enum_query_integer = null,
         ?float $enum_query_double = null,
-        array $enum_query_model_array = null,
-        array $enum_form_string_array = ['$'],
+        ?array $enum_query_model_array = null,
+        ?array $enum_form_string_array = ['$'],
         ?string $enum_form_string = '-efg',
         string $contentType = self::contentTypes['testEnumParameters'][0]
     ): array
@@ -4830,14 +4830,14 @@ class FakeApi
      * @return PromiseInterface
      */
     public function testEnumParametersAsync(
-        array $enum_header_string_array = ['$'],
+        ?array $enum_header_string_array = ['$'],
         ?string $enum_header_string = '-efg',
-        array $enum_query_string_array = ['$'],
+        ?array $enum_query_string_array = ['$'],
         ?string $enum_query_string = '-efg',
         ?int $enum_query_integer = null,
         ?float $enum_query_double = null,
-        array $enum_query_model_array = null,
-        array $enum_form_string_array = ['$'],
+        ?array $enum_query_model_array = null,
+        ?array $enum_form_string_array = ['$'],
         ?string $enum_form_string = '-efg',
         string $contentType = self::contentTypes['testEnumParameters'][0]
     ): PromiseInterface
@@ -4870,14 +4870,14 @@ class FakeApi
      * @return PromiseInterface
      */
     public function testEnumParametersAsyncWithHttpInfo(
-        array $enum_header_string_array = ['$'],
+        ?array $enum_header_string_array = ['$'],
         ?string $enum_header_string = '-efg',
-        array $enum_query_string_array = ['$'],
+        ?array $enum_query_string_array = ['$'],
         ?string $enum_query_string = '-efg',
         ?int $enum_query_integer = null,
         ?float $enum_query_double = null,
-        array $enum_query_model_array = null,
-        array $enum_form_string_array = ['$'],
+        ?array $enum_query_model_array = null,
+        ?array $enum_form_string_array = ['$'],
         ?string $enum_form_string = '-efg',
         string $contentType = self::contentTypes['testEnumParameters'][0]
     ): PromiseInterface
@@ -4926,14 +4926,14 @@ class FakeApi
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testEnumParametersRequest(
-        array $enum_header_string_array = ['$'],
+        ?array $enum_header_string_array = ['$'],
         ?string $enum_header_string = '-efg',
-        array $enum_query_string_array = ['$'],
+        ?array $enum_query_string_array = ['$'],
         ?string $enum_query_string = '-efg',
         ?int $enum_query_integer = null,
         ?float $enum_query_double = null,
-        array $enum_query_model_array = null,
-        array $enum_form_string_array = ['$'],
+        ?array $enum_query_model_array = null,
+        ?array $enum_form_string_array = ['$'],
         ?string $enum_form_string = '-efg',
         string $contentType = self::contentTypes['testEnumParameters'][0]
     ): Request
@@ -6369,7 +6369,7 @@ class FakeApi
         array $url,
         array $context,
         string $allow_empty,
-        array $language = null,
+        ?array $language = null,
         string $contentType = self::contentTypes['testQueryParameterCollectionFormat'][0]
     ): void
     {
@@ -6399,7 +6399,7 @@ class FakeApi
         array $url,
         array $context,
         string $allow_empty,
-        array $language = null,
+        ?array $language = null,
         string $contentType = self::contentTypes['testQueryParameterCollectionFormat'][0]
     ): array
     {
@@ -6459,7 +6459,7 @@ class FakeApi
         array $url,
         array $context,
         string $allow_empty,
-        array $language = null,
+        ?array $language = null,
         string $contentType = self::contentTypes['testQueryParameterCollectionFormat'][0]
     ): PromiseInterface
     {
@@ -6493,7 +6493,7 @@ class FakeApi
         array $url,
         array $context,
         string $allow_empty,
-        array $language = null,
+        ?array $language = null,
         string $contentType = self::contentTypes['testQueryParameterCollectionFormat'][0]
     ): PromiseInterface
     {
@@ -6545,7 +6545,7 @@ class FakeApi
         array $url,
         array $context,
         string $allow_empty,
-        array $language = null,
+        ?array $language = null,
         string $contentType = self::contentTypes['testQueryParameterCollectionFormat'][0]
     ): Request
     {
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/FakeClassnameTags123Api.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/FakeClassnameTags123Api.php
index 9b6248438e7..53aa2559585 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/FakeClassnameTags123Api.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/FakeClassnameTags123Api.php
@@ -83,9 +83,9 @@ class FakeClassnameTags123Api
      * @param int                  $hostIndex (Optional) host index to select the list of hosts if defined in the OpenAPI spec
      */
     public function __construct(
-        ClientInterface $client = null,
-        Configuration $config = null,
-        HeaderSelector $selector = null,
+        ?ClientInterface $client = null,
+        ?Configuration $config = null,
+        ?HeaderSelector $selector = null,
         int $hostIndex = 0
     ) {
         $this->client = $client ?: new Client();
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/PetApi.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/PetApi.php
index b67bfb33e71..ee8285375e5 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/PetApi.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/PetApi.php
@@ -109,9 +109,9 @@ class PetApi
      * @param int                  $hostIndex (Optional) host index to select the list of hosts if defined in the OpenAPI spec
      */
     public function __construct(
-        ClientInterface $client = null,
-        Configuration $config = null,
-        HeaderSelector $selector = null,
+        ?ClientInterface $client = null,
+        ?Configuration $config = null,
+        ?HeaderSelector $selector = null,
         int $hostIndex = 0
     ) {
         $this->client = $client ?: new Client();
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/StoreApi.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/StoreApi.php
index d94fa7e073a..61009b0cd62 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/StoreApi.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/StoreApi.php
@@ -92,9 +92,9 @@ class StoreApi
      * @param int                  $hostIndex (Optional) host index to select the list of hosts if defined in the OpenAPI spec
      */
     public function __construct(
-        ClientInterface $client = null,
-        Configuration $config = null,
-        HeaderSelector $selector = null,
+        ?ClientInterface $client = null,
+        ?Configuration $config = null,
+        ?HeaderSelector $selector = null,
         int $hostIndex = 0
     ) {
         $this->client = $client ?: new Client();
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/UserApi.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/UserApi.php
index e5912366560..9a899b720a8 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/UserApi.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/UserApi.php
@@ -104,9 +104,9 @@ class UserApi
      * @param int                  $hostIndex (Optional) host index to select the list of hosts if defined in the OpenAPI spec
      */
     public function __construct(
-        ClientInterface $client = null,
-        Configuration $config = null,
-        HeaderSelector $selector = null,
+        ?ClientInterface $client = null,
+        ?Configuration $config = null,
+        ?HeaderSelector $selector = null,
         int $hostIndex = 0
     ) {
         $this->client = $client ?: new Client();
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Configuration.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Configuration.php
index a0bb1a1f41f..64962fb0c9d 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Configuration.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Configuration.php
@@ -518,7 +518,7 @@ class Configuration
     * @param array|null $variables    hash of variable and the corresponding value (optional)
     * @return string URL based on host settings
     */
-    public static function getHostString(array $hostSettings, int $hostIndex, array $variables = null): string
+    public static function getHostString(array $hostSettings, int $hostIndex, ?array $variables = null): string
     {
         if (null === $variables) {
             $variables = [];
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/AdditionalPropertiesClass.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/AdditionalPropertiesClass.php
index c81ab29e9e3..a0818b4314f 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/AdditionalPropertiesClass.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/AdditionalPropertiesClass.php
@@ -246,7 +246,7 @@ class AdditionalPropertiesClass implements ModelInterface, ArrayAccess, JsonSeri
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('map_property', $data ?? [], null);
         $this->setIfExists('map_of_map_property', $data ?? [], null);
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/AllOfWithSingleRef.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/AllOfWithSingleRef.php
index be2c10d4b5d..3f8f5e57b83 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/AllOfWithSingleRef.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/AllOfWithSingleRef.php
@@ -246,7 +246,7 @@ class AllOfWithSingleRef implements ModelInterface, ArrayAccess, JsonSerializabl
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('username', $data ?? [], null);
         $this->setIfExists('single_ref_type', $data ?? [], null);
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Animal.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Animal.php
index 6cfe803a9b9..5a931370c4f 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Animal.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Animal.php
@@ -248,7 +248,7 @@ class Animal implements ModelInterface, ArrayAccess, JsonSerializable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         // Initialize discriminator property with the model name.
         $this->container['class_name'] = static::$openAPIModelName;
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ApiResponse.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ApiResponse.php
index 7de86f0d4d2..042c437e888 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ApiResponse.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ApiResponse.php
@@ -252,7 +252,7 @@ class ApiResponse implements ModelInterface, ArrayAccess, JsonSerializable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('code', $data ?? [], null);
         $this->setIfExists('type', $data ?? [], null);
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ArrayOfArrayOfNumberOnly.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ArrayOfArrayOfNumberOnly.php
index 417da0cb6e2..260a0b3fd62 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ArrayOfArrayOfNumberOnly.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ArrayOfArrayOfNumberOnly.php
@@ -240,7 +240,7 @@ class ArrayOfArrayOfNumberOnly implements ModelInterface, ArrayAccess, JsonSeria
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('array_array_number', $data ?? [], null);
     }
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ArrayOfNumberOnly.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ArrayOfNumberOnly.php
index 9c1f27734b5..eb5720b0c65 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ArrayOfNumberOnly.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ArrayOfNumberOnly.php
@@ -240,7 +240,7 @@ class ArrayOfNumberOnly implements ModelInterface, ArrayAccess, JsonSerializable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('array_number', $data ?? [], null);
     }
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ArrayTest.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ArrayTest.php
index ec5db2291a3..7fa35f704cf 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ArrayTest.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ArrayTest.php
@@ -252,7 +252,7 @@ class ArrayTest implements ModelInterface, ArrayAccess, JsonSerializable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('array_of_string', $data ?? [], null);
         $this->setIfExists('array_array_of_integer', $data ?? [], null);
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Capitalization.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Capitalization.php
index ee02084e4d4..c3eca4e7423 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Capitalization.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Capitalization.php
@@ -270,7 +270,7 @@ class Capitalization implements ModelInterface, ArrayAccess, JsonSerializable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('small_camel', $data ?? [], null);
         $this->setIfExists('capital_camel', $data ?? [], null);
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Cat.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Cat.php
index 617bdc45b5b..1bc509ef6bd 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Cat.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Cat.php
@@ -228,7 +228,7 @@ class Cat extends Animal
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         parent::__construct($data);
 
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Category.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Category.php
index 7d246661ff1..fc97e525e43 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Category.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Category.php
@@ -246,7 +246,7 @@ class Category implements ModelInterface, ArrayAccess, JsonSerializable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('id', $data ?? [], null);
         $this->setIfExists('name', $data ?? [], 'default-name');
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ChildWithNullable.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ChildWithNullable.php
index c78a1010ae3..f845483f922 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ChildWithNullable.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ChildWithNullable.php
@@ -228,7 +228,7 @@ class ChildWithNullable extends ParentWithNullable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         parent::__construct($data);
 
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ClassModel.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ClassModel.php
index 1f0f41c6882..6c889ae6493 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ClassModel.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ClassModel.php
@@ -241,7 +241,7 @@ class ClassModel implements ModelInterface, ArrayAccess, JsonSerializable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('_class', $data ?? [], null);
     }
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Client.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Client.php
index 0ab9cf654c6..20a718db68f 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Client.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Client.php
@@ -240,7 +240,7 @@ class Client implements ModelInterface, ArrayAccess, JsonSerializable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('client', $data ?? [], null);
     }
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/DeprecatedObject.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/DeprecatedObject.php
index 818f24803ea..1d4291efd61 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/DeprecatedObject.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/DeprecatedObject.php
@@ -240,7 +240,7 @@ class DeprecatedObject implements ModelInterface, ArrayAccess, JsonSerializable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('name', $data ?? [], null);
     }
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Dog.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Dog.php
index 869f3a31d66..58fa6961fad 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Dog.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Dog.php
@@ -228,7 +228,7 @@ class Dog extends Animal
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         parent::__construct($data);
 
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/EnumArrays.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/EnumArrays.php
index 32e7ddb1684..768bc547e37 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/EnumArrays.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/EnumArrays.php
@@ -276,7 +276,7 @@ class EnumArrays implements ModelInterface, ArrayAccess, JsonSerializable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('just_symbol', $data ?? [], null);
         $this->setIfExists('array_enum', $data ?? [], null);
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/EnumTest.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/EnumTest.php
index 5e5096d22ff..08faf3545da 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/EnumTest.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/EnumTest.php
@@ -346,7 +346,7 @@ class EnumTest implements ModelInterface, ArrayAccess, JsonSerializable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('enum_string', $data ?? [], null);
         $this->setIfExists('enum_string_required', $data ?? [], null);
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/FakeBigDecimalMap200Response.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/FakeBigDecimalMap200Response.php
index 26c1c581f84..5ffeeee32a6 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/FakeBigDecimalMap200Response.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/FakeBigDecimalMap200Response.php
@@ -246,7 +246,7 @@ class FakeBigDecimalMap200Response implements ModelInterface, ArrayAccess, JsonS
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('some_id', $data ?? [], null);
         $this->setIfExists('some_map', $data ?? [], null);
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/File.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/File.php
index 13c17600bdb..d2bc87c0c02 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/File.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/File.php
@@ -241,7 +241,7 @@ class File implements ModelInterface, ArrayAccess, JsonSerializable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('source_uri', $data ?? [], null);
     }
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/FileSchemaTestClass.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/FileSchemaTestClass.php
index cb590aca656..6c93793b718 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/FileSchemaTestClass.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/FileSchemaTestClass.php
@@ -246,7 +246,7 @@ class FileSchemaTestClass implements ModelInterface, ArrayAccess, JsonSerializab
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('file', $data ?? [], null);
         $this->setIfExists('files', $data ?? [], null);
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Foo.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Foo.php
index a09374e3127..c066a0a588f 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Foo.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Foo.php
@@ -240,7 +240,7 @@ class Foo implements ModelInterface, ArrayAccess, JsonSerializable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('bar', $data ?? [], 'bar');
     }
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/FooGetDefaultResponse.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/FooGetDefaultResponse.php
index 212876ee903..98a00ac34d5 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/FooGetDefaultResponse.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/FooGetDefaultResponse.php
@@ -240,7 +240,7 @@ class FooGetDefaultResponse implements ModelInterface, ArrayAccess, JsonSerializ
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('string', $data ?? [], null);
     }
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/FormatTest.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/FormatTest.php
index 55d06c91cf6..2f930b433a7 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/FormatTest.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/FormatTest.php
@@ -336,7 +336,7 @@ class FormatTest implements ModelInterface, ArrayAccess, JsonSerializable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('integer', $data ?? [], null);
         $this->setIfExists('int32', $data ?? [], null);
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/HasOnlyReadOnly.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/HasOnlyReadOnly.php
index d7f8fc2abc5..f7bfac6947c 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/HasOnlyReadOnly.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/HasOnlyReadOnly.php
@@ -246,7 +246,7 @@ class HasOnlyReadOnly implements ModelInterface, ArrayAccess, JsonSerializable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('bar', $data ?? [], null);
         $this->setIfExists('foo', $data ?? [], null);
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/HealthCheckResult.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/HealthCheckResult.php
index 246b9625fee..5ebe3d350de 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/HealthCheckResult.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/HealthCheckResult.php
@@ -241,7 +241,7 @@ class HealthCheckResult implements ModelInterface, ArrayAccess, JsonSerializable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('nullable_message', $data ?? [], null);
     }
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/MapTest.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/MapTest.php
index 562de395460..bcc7830daa1 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/MapTest.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/MapTest.php
@@ -273,7 +273,7 @@ class MapTest implements ModelInterface, ArrayAccess, JsonSerializable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('map_map_of_string', $data ?? [], null);
         $this->setIfExists('map_of_enum_string', $data ?? [], null);
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/MixedPropertiesAndAdditionalPropertiesClass.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/MixedPropertiesAndAdditionalPropertiesClass.php
index 34b95eff23f..9bdbf6a3b65 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/MixedPropertiesAndAdditionalPropertiesClass.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/MixedPropertiesAndAdditionalPropertiesClass.php
@@ -252,7 +252,7 @@ class MixedPropertiesAndAdditionalPropertiesClass implements ModelInterface, Arr
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('uuid', $data ?? [], null);
         $this->setIfExists('date_time', $data ?? [], null);
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Model200Response.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Model200Response.php
index f1257488aa9..0ec1e9af3cb 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Model200Response.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Model200Response.php
@@ -247,7 +247,7 @@ class Model200Response implements ModelInterface, ArrayAccess, JsonSerializable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('name', $data ?? [], null);
         $this->setIfExists('class', $data ?? [], null);
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ModelList.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ModelList.php
index 4e46e28726f..ec23cad4c46 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ModelList.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ModelList.php
@@ -240,7 +240,7 @@ class ModelList implements ModelInterface, ArrayAccess, JsonSerializable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('_123_list', $data ?? [], null);
     }
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ModelReturn.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ModelReturn.php
index a07bf74896b..dad11ea5fd6 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ModelReturn.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ModelReturn.php
@@ -241,7 +241,7 @@ class ModelReturn implements ModelInterface, ArrayAccess, JsonSerializable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('return', $data ?? [], null);
     }
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Name.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Name.php
index 62d63c87317..afc0703954a 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Name.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Name.php
@@ -259,7 +259,7 @@ class Name implements ModelInterface, ArrayAccess, JsonSerializable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('name', $data ?? [], null);
         $this->setIfExists('snake_case', $data ?? [], null);
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/NullableClass.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/NullableClass.php
index 25af6b83c3f..f72dbe0f55a 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/NullableClass.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/NullableClass.php
@@ -306,7 +306,7 @@ class NullableClass implements ModelInterface, ArrayAccess, JsonSerializable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('integer_prop', $data ?? [], null);
         $this->setIfExists('number_prop', $data ?? [], null);
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/NumberOnly.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/NumberOnly.php
index a7110c6069a..08967bb822a 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/NumberOnly.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/NumberOnly.php
@@ -240,7 +240,7 @@ class NumberOnly implements ModelInterface, ArrayAccess, JsonSerializable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('just_number', $data ?? [], null);
     }
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ObjectWithDeprecatedFields.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ObjectWithDeprecatedFields.php
index fb50b7521e8..4c874a96e68 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ObjectWithDeprecatedFields.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ObjectWithDeprecatedFields.php
@@ -258,7 +258,7 @@ class ObjectWithDeprecatedFields implements ModelInterface, ArrayAccess, JsonSer
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('uuid', $data ?? [], null);
         $this->setIfExists('id', $data ?? [], null);
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Order.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Order.php
index 04081a19f9a..53824f659cb 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Order.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Order.php
@@ -287,7 +287,7 @@ class Order implements ModelInterface, ArrayAccess, JsonSerializable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('id', $data ?? [], null);
         $this->setIfExists('pet_id', $data ?? [], null);
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/OuterComposite.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/OuterComposite.php
index e40f6ac0f4c..c5885c5aed1 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/OuterComposite.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/OuterComposite.php
@@ -252,7 +252,7 @@ class OuterComposite implements ModelInterface, ArrayAccess, JsonSerializable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('my_number', $data ?? [], null);
         $this->setIfExists('my_string', $data ?? [], null);
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/OuterObjectWithEnumProperty.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/OuterObjectWithEnumProperty.php
index c6f2a03d534..6421e5382b9 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/OuterObjectWithEnumProperty.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/OuterObjectWithEnumProperty.php
@@ -240,7 +240,7 @@ class OuterObjectWithEnumProperty implements ModelInterface, ArrayAccess, JsonSe
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('value', $data ?? [], null);
     }
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ParentWithNullable.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ParentWithNullable.php
index 861f2c6e718..873fd9f5936 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ParentWithNullable.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ParentWithNullable.php
@@ -259,7 +259,7 @@ class ParentWithNullable implements ModelInterface, ArrayAccess, JsonSerializabl
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         // Initialize discriminator property with the model name.
         $this->container['type'] = static::$openAPIModelName;
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Pet.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Pet.php
index f2ebc9206da..d75e2ea8d33 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Pet.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Pet.php
@@ -287,7 +287,7 @@ class Pet implements ModelInterface, ArrayAccess, JsonSerializable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('id', $data ?? [], null);
         $this->setIfExists('category', $data ?? [], null);
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ReadOnlyFirst.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ReadOnlyFirst.php
index 039f6758c51..8808d8e5c6c 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ReadOnlyFirst.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/ReadOnlyFirst.php
@@ -246,7 +246,7 @@ class ReadOnlyFirst implements ModelInterface, ArrayAccess, JsonSerializable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('bar', $data ?? [], null);
         $this->setIfExists('baz', $data ?? [], null);
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/SpecialModelName.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/SpecialModelName.php
index fc3091cecd6..15bd3d9b5cb 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/SpecialModelName.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/SpecialModelName.php
@@ -240,7 +240,7 @@ class SpecialModelName implements ModelInterface, ArrayAccess, JsonSerializable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('special_property_name', $data ?? [], null);
     }
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Tag.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Tag.php
index 302b72d4708..f8c499f80a0 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Tag.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/Tag.php
@@ -246,7 +246,7 @@ class Tag implements ModelInterface, ArrayAccess, JsonSerializable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('id', $data ?? [], null);
         $this->setIfExists('name', $data ?? [], null);
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/TestInlineFreeformAdditionalPropertiesRequest.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/TestInlineFreeformAdditionalPropertiesRequest.php
index 62b9efe2f90..90128005e60 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/TestInlineFreeformAdditionalPropertiesRequest.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/TestInlineFreeformAdditionalPropertiesRequest.php
@@ -240,7 +240,7 @@ class TestInlineFreeformAdditionalPropertiesRequest implements ModelInterface, A
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('some_property', $data ?? [], null);
     }
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/User.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/User.php
index e216ccc66fc..c1fe348b10d 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/User.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Model/User.php
@@ -282,7 +282,7 @@ class User implements ModelInterface, ArrayAccess, JsonSerializable
      *
      * @param array $data Associated array of property values initializing the model
      */
-    public function __construct(array $data = null)
+    public function __construct(?array $data = null)
     {
         $this->setIfExists('id', $data ?? [], null);
         $this->setIfExists('username', $data ?? [], null);
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/ObjectSerializer.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/ObjectSerializer.php
index ee1b535f18c..87b20e656bf 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/ObjectSerializer.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/ObjectSerializer.php
@@ -65,7 +65,7 @@ class ObjectSerializer
      *
      * @return scalar|object|array|null serialized form of $data
      */
-    public static function sanitizeForSerialization(mixed $data, string $type = null, string $format = null): mixed
+    public static function sanitizeForSerialization(mixed $data, ?string $type = null, ?string $format = null): mixed
     {
         if (is_scalar($data) || null === $data) {
             return $data;
@@ -397,7 +397,7 @@ class ObjectSerializer
      *
      * @return mixed a single or an array of $class instances
      */
-    public static function deserialize(mixed $data, string $class, array $httpHeaders = null): mixed
+    public static function deserialize(mixed $data, string $class, ?array $httpHeaders = null): mixed
     {
         if (null === $data) {
             return null;
diff --git a/samples/server/petstore/php-mezzio-ph-modern/src/App/Factory.php b/samples/server/petstore/php-mezzio-ph-modern/src/App/Factory.php
index 24eb21b492c..d0a810b86c6 100644
--- a/samples/server/petstore/php-mezzio-ph-modern/src/App/Factory.php
+++ b/samples/server/petstore/php-mezzio-ph-modern/src/App/Factory.php
@@ -21,7 +21,7 @@ use Laminas\Stratigility\MiddlewarePipe;
 
 class Factory implements FactoryInterface
 {
-    public function __invoke(ContainerInterface $container, $requestedName, array $options = null): Application
+    public function __invoke(ContainerInterface $container, $requestedName, ?array $options = null): Application
     {
         $errorMiddleware = self::getErrorMiddleware($container);
         $pipeline = new MiddlewarePipe();
diff --git a/samples/server/petstore/php-mezzio-ph/src/App/Factory.php b/samples/server/petstore/php-mezzio-ph/src/App/Factory.php
index 8cfe7e295af..87ef7a91822 100644
--- a/samples/server/petstore/php-mezzio-ph/src/App/Factory.php
+++ b/samples/server/petstore/php-mezzio-ph/src/App/Factory.php
@@ -21,7 +21,7 @@ use Laminas\Stratigility\MiddlewarePipe;
 
 class Factory implements FactoryInterface
 {
-    public function __invoke(ContainerInterface $container, $requestedName, array $options = null): Application
+    public function __invoke(ContainerInterface $container, $requestedName, ?array $options = null): Application
     {
         $errorMiddleware = self::getErrorMiddleware($container);
         $pipeline = new MiddlewarePipe();