diff --git a/modules/openapi-generator/src/main/resources/php/ModelInterface.mustache b/modules/openapi-generator/src/main/resources/php/ModelInterface.mustache
index e13fc20411e..805db43f0df 100644
--- a/modules/openapi-generator/src/main/resources/php/ModelInterface.mustache
+++ b/modules/openapi-generator/src/main/resources/php/ModelInterface.mustache
@@ -83,4 +83,20 @@ interface ModelInterface
      * @return bool
      */
     public function valid();
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool;
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool;
 }
diff --git a/modules/openapi-generator/src/main/resources/php/ObjectSerializer.mustache b/modules/openapi-generator/src/main/resources/php/ObjectSerializer.mustache
index 2c6aa836fb9..6b27c09d5f4 100644
--- a/modules/openapi-generator/src/main/resources/php/ObjectSerializer.mustache
+++ b/modules/openapi-generator/src/main/resources/php/ObjectSerializer.mustache
@@ -89,7 +89,7 @@ class ObjectSerializer
                             }
                         }
                     }
-                    if ($value !== null) {
+                    if (($data::isNullable($property) && $data->isNullableSetToNull($property)) || $value !== null) {
                         $values[$data::attributeMap()[$property]] = self::sanitizeForSerialization($value, $openAPIType, $formats[$property]);
                     }
                 }
@@ -460,7 +460,15 @@ class ObjectSerializer
             foreach ($instance::openAPITypes() as $property => $type) {
                 $propertySetter = $instance::setters()[$property];
 
-                if (!isset($propertySetter) || !isset($data->{$instance::attributeMap()[$property]})) {
+                if (!isset($propertySetter)) {
+                    continue;
+                }
+
+                if (!isset($data->{$instance::attributeMap()[$property]})) {
+                    if ($instance::isNullable($property)) {
+                        $instance->$propertySetter(null);
+                    }
+
                     continue;
                 }
 
diff --git a/modules/openapi-generator/src/main/resources/php/model_generic.mustache b/modules/openapi-generator/src/main/resources/php/model_generic.mustache
index 9f6bdaa649a..f09167eaa89 100644
--- a/modules/openapi-generator/src/main/resources/php/model_generic.mustache
+++ b/modules/openapi-generator/src/main/resources/php/model_generic.mustache
@@ -31,6 +31,23 @@ class {{classname}} {{#parentSchema}}extends {{{parent}}}{{/parentSchema}}{{^par
         {{/-last}}{{/vars}}
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        {{#vars}}'{{name}}' => {{#isNullable}}true{{/isNullable}}{{^isNullable}}false{{/isNullable}}{{^-last}},
+		{{/-last}}{{/vars}}
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -51,6 +68,48 @@ class {{classname}} {{#parentSchema}}extends {{{parent}}}{{/parentSchema}}{{^par
         return self::$openAPIFormats{{#parentSchema}} + parent::openAPIFormats(){{/parentSchema}};
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables{{#parentSchema}} + parent::openAPINullables(){{/parentSchema}};
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -172,7 +231,7 @@ class {{classname}} {{#parentSchema}}extends {{{parent}}}{{/parentSchema}}{{^par
 
         {{/parentSchema}}
         {{#vars}}
-        $this->container['{{name}}'] = $data['{{name}}'] ?? {{{defaultValue}}}{{^defaultValue}}null{{/defaultValue}};
+        $this->setIfExists('{{name}}', $data ?? [], {{#defaultValue}}{{{defaultValue}}}{{/defaultValue}}{{^defaultValue}}null{{/defaultValue}});
         {{/vars}}
         {{#discriminator}}
 
@@ -181,6 +240,24 @@ class {{classname}} {{#parentSchema}}extends {{{parent}}}{{/parentSchema}}{{^par
         {{/discriminator}}
     }
 
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
+    }
+
     /**
      * Show all the invalid properties with reasons.
      *
@@ -359,6 +436,25 @@ class {{classname}} {{#parentSchema}}extends {{{parent}}}{{/parentSchema}}{{^par
         }
         {{/minItems}}
         {{/hasValidation}}
+
+        {{#isNullable}}
+        if (is_null(${{name}})) {
+            array_push($this->openAPINullablesSetToNull, '{{name}}');
+        } else {
+            $nullablesSetToNull = $this->getOpenAPINullablesSetToNull();
+            $index = array_search('{{name}}', $nullablesSetToNull);
+            if ($index !== FALSE) {
+                unset($nullablesSetToNull[$index]);
+                $this->setOpenAPINullablesSetToNull($nullablesSetToNull);
+            }
+        }
+        {{/isNullable}}
+        {{^isNullable}}
+        if (is_null(${{name}})) {
+            throw new \InvalidArgumentException('non-nullable {{name}} cannot be null');
+        }
+        {{/isNullable}}
+
         $this->container['{{name}}'] = ${{name}};
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/AdditionalPropertiesClass.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/AdditionalPropertiesClass.php
index 9aed83a3e41..a8f964b20a1 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/AdditionalPropertiesClass.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/AdditionalPropertiesClass.php
@@ -73,6 +73,23 @@ class AdditionalPropertiesClass implements ModelInterface, ArrayAccess, \JsonSer
         'map_of_map_property' => null
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        'map_property' => false,
+		'map_of_map_property' => false
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -93,6 +110,48 @@ class AdditionalPropertiesClass implements ModelInterface, ArrayAccess, \JsonSer
         return self::$openAPIFormats;
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables;
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -181,8 +240,26 @@ class AdditionalPropertiesClass implements ModelInterface, ArrayAccess, \JsonSer
      */
     public function __construct(array $data = null)
     {
-        $this->container['map_property'] = $data['map_property'] ?? null;
-        $this->container['map_of_map_property'] = $data['map_of_map_property'] ?? null;
+        $this->setIfExists('map_property', $data ?? [], null);
+        $this->setIfExists('map_of_map_property', $data ?? [], null);
+    }
+
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
     }
 
     /**
@@ -228,6 +305,11 @@ class AdditionalPropertiesClass implements ModelInterface, ArrayAccess, \JsonSer
      */
     public function setMapProperty($map_property)
     {
+
+        if (is_null($map_property)) {
+            throw new \InvalidArgumentException('non-nullable map_property cannot be null');
+        }
+
         $this->container['map_property'] = $map_property;
 
         return $this;
@@ -252,6 +334,11 @@ class AdditionalPropertiesClass implements ModelInterface, ArrayAccess, \JsonSer
      */
     public function setMapOfMapProperty($map_of_map_property)
     {
+
+        if (is_null($map_of_map_property)) {
+            throw new \InvalidArgumentException('non-nullable map_of_map_property cannot be null');
+        }
+
         $this->container['map_of_map_property'] = $map_of_map_property;
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/AllOfWithSingleRef.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/AllOfWithSingleRef.php
index 31a8ac52f03..3c6fa68e2bf 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/AllOfWithSingleRef.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/AllOfWithSingleRef.php
@@ -73,6 +73,23 @@ class AllOfWithSingleRef implements ModelInterface, ArrayAccess, \JsonSerializab
         'single_ref_type' => null
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        'username' => false,
+		'single_ref_type' => true
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -93,6 +110,48 @@ class AllOfWithSingleRef implements ModelInterface, ArrayAccess, \JsonSerializab
         return self::$openAPIFormats;
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables;
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -181,8 +240,26 @@ class AllOfWithSingleRef implements ModelInterface, ArrayAccess, \JsonSerializab
      */
     public function __construct(array $data = null)
     {
-        $this->container['username'] = $data['username'] ?? null;
-        $this->container['single_ref_type'] = $data['single_ref_type'] ?? null;
+        $this->setIfExists('username', $data ?? [], null);
+        $this->setIfExists('single_ref_type', $data ?? [], null);
+    }
+
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
     }
 
     /**
@@ -228,6 +305,11 @@ class AllOfWithSingleRef implements ModelInterface, ArrayAccess, \JsonSerializab
      */
     public function setUsername($username)
     {
+
+        if (is_null($username)) {
+            throw new \InvalidArgumentException('non-nullable username cannot be null');
+        }
+
         $this->container['username'] = $username;
 
         return $this;
@@ -252,6 +334,18 @@ class AllOfWithSingleRef implements ModelInterface, ArrayAccess, \JsonSerializab
      */
     public function setSingleRefType($single_ref_type)
     {
+
+        if (is_null($single_ref_type)) {
+            array_push($this->openAPINullablesSetToNull, 'single_ref_type');
+        } else {
+            $nullablesSetToNull = $this->getOpenAPINullablesSetToNull();
+            $index = array_search('single_ref_type', $nullablesSetToNull);
+            if ($index !== FALSE) {
+                unset($nullablesSetToNull[$index]);
+                $this->setOpenAPINullablesSetToNull($nullablesSetToNull);
+            }
+        }
+
         $this->container['single_ref_type'] = $single_ref_type;
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Animal.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Animal.php
index 3de3eb9aacf..d68059ec45c 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Animal.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Animal.php
@@ -73,6 +73,23 @@ class Animal implements ModelInterface, ArrayAccess, \JsonSerializable
         'color' => null
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        'class_name' => false,
+		'color' => false
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -93,6 +110,48 @@ class Animal implements ModelInterface, ArrayAccess, \JsonSerializable
         return self::$openAPIFormats;
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables;
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -181,13 +240,31 @@ class Animal implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function __construct(array $data = null)
     {
-        $this->container['class_name'] = $data['class_name'] ?? null;
-        $this->container['color'] = $data['color'] ?? 'red';
+        $this->setIfExists('class_name', $data ?? [], null);
+        $this->setIfExists('color', $data ?? [], 'red');
 
         // Initialize discriminator property with the model name.
         $this->container['class_name'] = static::$openAPIModelName;
     }
 
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
+    }
+
     /**
      * Show all the invalid properties with reasons.
      *
@@ -234,6 +311,11 @@ class Animal implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setClassName($class_name)
     {
+
+        if (is_null($class_name)) {
+            throw new \InvalidArgumentException('non-nullable class_name cannot be null');
+        }
+
         $this->container['class_name'] = $class_name;
 
         return $this;
@@ -258,6 +340,11 @@ class Animal implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setColor($color)
     {
+
+        if (is_null($color)) {
+            throw new \InvalidArgumentException('non-nullable color cannot be null');
+        }
+
         $this->container['color'] = $color;
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ApiResponse.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ApiResponse.php
index e391f008a0d..b2d7029b44d 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ApiResponse.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ApiResponse.php
@@ -75,6 +75,24 @@ class ApiResponse implements ModelInterface, ArrayAccess, \JsonSerializable
         'message' => null
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        'code' => false,
+		'type' => false,
+		'message' => false
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -95,6 +113,48 @@ class ApiResponse implements ModelInterface, ArrayAccess, \JsonSerializable
         return self::$openAPIFormats;
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables;
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -186,9 +246,27 @@ class ApiResponse implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function __construct(array $data = null)
     {
-        $this->container['code'] = $data['code'] ?? null;
-        $this->container['type'] = $data['type'] ?? null;
-        $this->container['message'] = $data['message'] ?? null;
+        $this->setIfExists('code', $data ?? [], null);
+        $this->setIfExists('type', $data ?? [], null);
+        $this->setIfExists('message', $data ?? [], null);
+    }
+
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
     }
 
     /**
@@ -234,6 +312,11 @@ class ApiResponse implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setCode($code)
     {
+
+        if (is_null($code)) {
+            throw new \InvalidArgumentException('non-nullable code cannot be null');
+        }
+
         $this->container['code'] = $code;
 
         return $this;
@@ -258,6 +341,11 @@ class ApiResponse implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setType($type)
     {
+
+        if (is_null($type)) {
+            throw new \InvalidArgumentException('non-nullable type cannot be null');
+        }
+
         $this->container['type'] = $type;
 
         return $this;
@@ -282,6 +370,11 @@ class ApiResponse implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setMessage($message)
     {
+
+        if (is_null($message)) {
+            throw new \InvalidArgumentException('non-nullable message cannot be null');
+        }
+
         $this->container['message'] = $message;
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ArrayOfArrayOfNumberOnly.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ArrayOfArrayOfNumberOnly.php
index cbeeb23f199..aed58a032e9 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ArrayOfArrayOfNumberOnly.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ArrayOfArrayOfNumberOnly.php
@@ -71,6 +71,22 @@ class ArrayOfArrayOfNumberOnly implements ModelInterface, ArrayAccess, \JsonSeri
         'array_array_number' => null
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        'array_array_number' => false
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -91,6 +107,48 @@ class ArrayOfArrayOfNumberOnly implements ModelInterface, ArrayAccess, \JsonSeri
         return self::$openAPIFormats;
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables;
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -176,7 +234,25 @@ class ArrayOfArrayOfNumberOnly implements ModelInterface, ArrayAccess, \JsonSeri
      */
     public function __construct(array $data = null)
     {
-        $this->container['array_array_number'] = $data['array_array_number'] ?? null;
+        $this->setIfExists('array_array_number', $data ?? [], null);
+    }
+
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
     }
 
     /**
@@ -222,6 +298,11 @@ class ArrayOfArrayOfNumberOnly implements ModelInterface, ArrayAccess, \JsonSeri
      */
     public function setArrayArrayNumber($array_array_number)
     {
+
+        if (is_null($array_array_number)) {
+            throw new \InvalidArgumentException('non-nullable array_array_number cannot be null');
+        }
+
         $this->container['array_array_number'] = $array_array_number;
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ArrayOfNumberOnly.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ArrayOfNumberOnly.php
index ff01b1f34af..13e1bf8f46a 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ArrayOfNumberOnly.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ArrayOfNumberOnly.php
@@ -71,6 +71,22 @@ class ArrayOfNumberOnly implements ModelInterface, ArrayAccess, \JsonSerializabl
         'array_number' => null
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        'array_number' => false
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -91,6 +107,48 @@ class ArrayOfNumberOnly implements ModelInterface, ArrayAccess, \JsonSerializabl
         return self::$openAPIFormats;
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables;
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -176,7 +234,25 @@ class ArrayOfNumberOnly implements ModelInterface, ArrayAccess, \JsonSerializabl
      */
     public function __construct(array $data = null)
     {
-        $this->container['array_number'] = $data['array_number'] ?? null;
+        $this->setIfExists('array_number', $data ?? [], null);
+    }
+
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
     }
 
     /**
@@ -222,6 +298,11 @@ class ArrayOfNumberOnly implements ModelInterface, ArrayAccess, \JsonSerializabl
      */
     public function setArrayNumber($array_number)
     {
+
+        if (is_null($array_number)) {
+            throw new \InvalidArgumentException('non-nullable array_number cannot be null');
+        }
+
         $this->container['array_number'] = $array_number;
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ArrayTest.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ArrayTest.php
index 651a1fe61b3..b74e89e8e83 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ArrayTest.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ArrayTest.php
@@ -75,6 +75,24 @@ class ArrayTest implements ModelInterface, ArrayAccess, \JsonSerializable
         'array_array_of_model' => null
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        'array_of_string' => false,
+		'array_array_of_integer' => false,
+		'array_array_of_model' => false
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -95,6 +113,48 @@ class ArrayTest implements ModelInterface, ArrayAccess, \JsonSerializable
         return self::$openAPIFormats;
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables;
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -186,9 +246,27 @@ class ArrayTest implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function __construct(array $data = null)
     {
-        $this->container['array_of_string'] = $data['array_of_string'] ?? null;
-        $this->container['array_array_of_integer'] = $data['array_array_of_integer'] ?? null;
-        $this->container['array_array_of_model'] = $data['array_array_of_model'] ?? null;
+        $this->setIfExists('array_of_string', $data ?? [], null);
+        $this->setIfExists('array_array_of_integer', $data ?? [], null);
+        $this->setIfExists('array_array_of_model', $data ?? [], null);
+    }
+
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
     }
 
     /**
@@ -249,6 +327,11 @@ class ArrayTest implements ModelInterface, ArrayAccess, \JsonSerializable
         if (!is_null($array_of_string) && (count($array_of_string) < 0)) {
             throw new \InvalidArgumentException('invalid length for $array_of_string when calling ArrayTest., number of items must be greater than or equal to 0.');
         }
+
+        if (is_null($array_of_string)) {
+            throw new \InvalidArgumentException('non-nullable array_of_string cannot be null');
+        }
+
         $this->container['array_of_string'] = $array_of_string;
 
         return $this;
@@ -273,6 +356,11 @@ class ArrayTest implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setArrayArrayOfInteger($array_array_of_integer)
     {
+
+        if (is_null($array_array_of_integer)) {
+            throw new \InvalidArgumentException('non-nullable array_array_of_integer cannot be null');
+        }
+
         $this->container['array_array_of_integer'] = $array_array_of_integer;
 
         return $this;
@@ -297,6 +385,11 @@ class ArrayTest implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setArrayArrayOfModel($array_array_of_model)
     {
+
+        if (is_null($array_array_of_model)) {
+            throw new \InvalidArgumentException('non-nullable array_array_of_model cannot be null');
+        }
+
         $this->container['array_array_of_model'] = $array_array_of_model;
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Capitalization.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Capitalization.php
index 222ea4d21ce..074096f0f80 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Capitalization.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Capitalization.php
@@ -81,6 +81,27 @@ class Capitalization implements ModelInterface, ArrayAccess, \JsonSerializable
         'att_name' => null
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        'small_camel' => false,
+		'capital_camel' => false,
+		'small_snake' => false,
+		'capital_snake' => false,
+		'sca_eth_flow_points' => false,
+		'att_name' => false
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -101,6 +122,48 @@ class Capitalization implements ModelInterface, ArrayAccess, \JsonSerializable
         return self::$openAPIFormats;
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables;
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -201,12 +264,30 @@ class Capitalization implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function __construct(array $data = null)
     {
-        $this->container['small_camel'] = $data['small_camel'] ?? null;
-        $this->container['capital_camel'] = $data['capital_camel'] ?? null;
-        $this->container['small_snake'] = $data['small_snake'] ?? null;
-        $this->container['capital_snake'] = $data['capital_snake'] ?? null;
-        $this->container['sca_eth_flow_points'] = $data['sca_eth_flow_points'] ?? null;
-        $this->container['att_name'] = $data['att_name'] ?? null;
+        $this->setIfExists('small_camel', $data ?? [], null);
+        $this->setIfExists('capital_camel', $data ?? [], null);
+        $this->setIfExists('small_snake', $data ?? [], null);
+        $this->setIfExists('capital_snake', $data ?? [], null);
+        $this->setIfExists('sca_eth_flow_points', $data ?? [], null);
+        $this->setIfExists('att_name', $data ?? [], null);
+    }
+
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
     }
 
     /**
@@ -252,6 +333,11 @@ class Capitalization implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setSmallCamel($small_camel)
     {
+
+        if (is_null($small_camel)) {
+            throw new \InvalidArgumentException('non-nullable small_camel cannot be null');
+        }
+
         $this->container['small_camel'] = $small_camel;
 
         return $this;
@@ -276,6 +362,11 @@ class Capitalization implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setCapitalCamel($capital_camel)
     {
+
+        if (is_null($capital_camel)) {
+            throw new \InvalidArgumentException('non-nullable capital_camel cannot be null');
+        }
+
         $this->container['capital_camel'] = $capital_camel;
 
         return $this;
@@ -300,6 +391,11 @@ class Capitalization implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setSmallSnake($small_snake)
     {
+
+        if (is_null($small_snake)) {
+            throw new \InvalidArgumentException('non-nullable small_snake cannot be null');
+        }
+
         $this->container['small_snake'] = $small_snake;
 
         return $this;
@@ -324,6 +420,11 @@ class Capitalization implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setCapitalSnake($capital_snake)
     {
+
+        if (is_null($capital_snake)) {
+            throw new \InvalidArgumentException('non-nullable capital_snake cannot be null');
+        }
+
         $this->container['capital_snake'] = $capital_snake;
 
         return $this;
@@ -348,6 +449,11 @@ class Capitalization implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setScaEthFlowPoints($sca_eth_flow_points)
     {
+
+        if (is_null($sca_eth_flow_points)) {
+            throw new \InvalidArgumentException('non-nullable sca_eth_flow_points cannot be null');
+        }
+
         $this->container['sca_eth_flow_points'] = $sca_eth_flow_points;
 
         return $this;
@@ -372,6 +478,11 @@ class Capitalization implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setAttName($att_name)
     {
+
+        if (is_null($att_name)) {
+            throw new \InvalidArgumentException('non-nullable att_name cannot be null');
+        }
+
         $this->container['att_name'] = $att_name;
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Cat.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Cat.php
index f60f2381aa5..b619f458da6 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Cat.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Cat.php
@@ -69,6 +69,22 @@ class Cat extends Animal
         'declawed' => null
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        'declawed' => false
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -89,6 +105,48 @@ class Cat extends Animal
         return self::$openAPIFormats + parent::openAPIFormats();
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables + parent::openAPINullables();
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -170,7 +228,25 @@ class Cat extends Animal
     {
         parent::__construct($data);
 
-        $this->container['declawed'] = $data['declawed'] ?? null;
+        $this->setIfExists('declawed', $data ?? [], null);
+    }
+
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
     }
 
     /**
@@ -216,6 +292,11 @@ class Cat extends Animal
      */
     public function setDeclawed($declawed)
     {
+
+        if (is_null($declawed)) {
+            throw new \InvalidArgumentException('non-nullable declawed cannot be null');
+        }
+
         $this->container['declawed'] = $declawed;
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/CatAllOf.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/CatAllOf.php
index d0e6f619555..1388eedf634 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/CatAllOf.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/CatAllOf.php
@@ -71,6 +71,22 @@ class CatAllOf implements ModelInterface, ArrayAccess, \JsonSerializable
         'declawed' => null
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        'declawed' => false
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -91,6 +107,48 @@ class CatAllOf implements ModelInterface, ArrayAccess, \JsonSerializable
         return self::$openAPIFormats;
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables;
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -176,7 +234,25 @@ class CatAllOf implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function __construct(array $data = null)
     {
-        $this->container['declawed'] = $data['declawed'] ?? null;
+        $this->setIfExists('declawed', $data ?? [], null);
+    }
+
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
     }
 
     /**
@@ -222,6 +298,11 @@ class CatAllOf implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setDeclawed($declawed)
     {
+
+        if (is_null($declawed)) {
+            throw new \InvalidArgumentException('non-nullable declawed cannot be null');
+        }
+
         $this->container['declawed'] = $declawed;
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Category.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Category.php
index 6726c381360..0b3b4e92d6a 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Category.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Category.php
@@ -73,6 +73,23 @@ class Category implements ModelInterface, ArrayAccess, \JsonSerializable
         'name' => null
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        'id' => false,
+		'name' => false
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -93,6 +110,48 @@ class Category implements ModelInterface, ArrayAccess, \JsonSerializable
         return self::$openAPIFormats;
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables;
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -181,8 +240,26 @@ class Category implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function __construct(array $data = null)
     {
-        $this->container['id'] = $data['id'] ?? null;
-        $this->container['name'] = $data['name'] ?? 'default-name';
+        $this->setIfExists('id', $data ?? [], null);
+        $this->setIfExists('name', $data ?? [], 'default-name');
+    }
+
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
     }
 
     /**
@@ -231,6 +308,11 @@ class Category implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setId($id)
     {
+
+        if (is_null($id)) {
+            throw new \InvalidArgumentException('non-nullable id cannot be null');
+        }
+
         $this->container['id'] = $id;
 
         return $this;
@@ -255,6 +337,11 @@ class Category implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setName($name)
     {
+
+        if (is_null($name)) {
+            throw new \InvalidArgumentException('non-nullable name cannot be null');
+        }
+
         $this->container['name'] = $name;
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ClassModel.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ClassModel.php
index 3c84b6f4db6..c756c20e665 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ClassModel.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ClassModel.php
@@ -72,6 +72,22 @@ class ClassModel implements ModelInterface, ArrayAccess, \JsonSerializable
         '_class' => null
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        '_class' => false
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -92,6 +108,48 @@ class ClassModel implements ModelInterface, ArrayAccess, \JsonSerializable
         return self::$openAPIFormats;
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables;
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -177,7 +235,25 @@ class ClassModel implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function __construct(array $data = null)
     {
-        $this->container['_class'] = $data['_class'] ?? null;
+        $this->setIfExists('_class', $data ?? [], null);
+    }
+
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
     }
 
     /**
@@ -223,6 +299,11 @@ class ClassModel implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setClass($_class)
     {
+
+        if (is_null($_class)) {
+            throw new \InvalidArgumentException('non-nullable _class cannot be null');
+        }
+
         $this->container['_class'] = $_class;
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Client.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Client.php
index e0cd800b055..4a538595f81 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Client.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Client.php
@@ -71,6 +71,22 @@ class Client implements ModelInterface, ArrayAccess, \JsonSerializable
         'client' => null
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        'client' => false
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -91,6 +107,48 @@ class Client implements ModelInterface, ArrayAccess, \JsonSerializable
         return self::$openAPIFormats;
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables;
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -176,7 +234,25 @@ class Client implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function __construct(array $data = null)
     {
-        $this->container['client'] = $data['client'] ?? null;
+        $this->setIfExists('client', $data ?? [], null);
+    }
+
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
     }
 
     /**
@@ -222,6 +298,11 @@ class Client implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setClient($client)
     {
+
+        if (is_null($client)) {
+            throw new \InvalidArgumentException('non-nullable client cannot be null');
+        }
+
         $this->container['client'] = $client;
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/DeprecatedObject.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/DeprecatedObject.php
index 2313c50719f..3d07cc7266a 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/DeprecatedObject.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/DeprecatedObject.php
@@ -71,6 +71,22 @@ class DeprecatedObject implements ModelInterface, ArrayAccess, \JsonSerializable
         'name' => null
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        'name' => false
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -91,6 +107,48 @@ class DeprecatedObject implements ModelInterface, ArrayAccess, \JsonSerializable
         return self::$openAPIFormats;
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables;
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -176,7 +234,25 @@ class DeprecatedObject implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function __construct(array $data = null)
     {
-        $this->container['name'] = $data['name'] ?? null;
+        $this->setIfExists('name', $data ?? [], null);
+    }
+
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
     }
 
     /**
@@ -222,6 +298,11 @@ class DeprecatedObject implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setName($name)
     {
+
+        if (is_null($name)) {
+            throw new \InvalidArgumentException('non-nullable name cannot be null');
+        }
+
         $this->container['name'] = $name;
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Dog.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Dog.php
index b7bfcfb7071..a305a4a79c5 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Dog.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Dog.php
@@ -69,6 +69,22 @@ class Dog extends Animal
         'breed' => null
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        'breed' => false
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -89,6 +105,48 @@ class Dog extends Animal
         return self::$openAPIFormats + parent::openAPIFormats();
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables + parent::openAPINullables();
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -170,7 +228,25 @@ class Dog extends Animal
     {
         parent::__construct($data);
 
-        $this->container['breed'] = $data['breed'] ?? null;
+        $this->setIfExists('breed', $data ?? [], null);
+    }
+
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
     }
 
     /**
@@ -216,6 +292,11 @@ class Dog extends Animal
      */
     public function setBreed($breed)
     {
+
+        if (is_null($breed)) {
+            throw new \InvalidArgumentException('non-nullable breed cannot be null');
+        }
+
         $this->container['breed'] = $breed;
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/DogAllOf.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/DogAllOf.php
index 9d81debc4e0..c8b8fb7e736 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/DogAllOf.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/DogAllOf.php
@@ -71,6 +71,22 @@ class DogAllOf implements ModelInterface, ArrayAccess, \JsonSerializable
         'breed' => null
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        'breed' => false
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -91,6 +107,48 @@ class DogAllOf implements ModelInterface, ArrayAccess, \JsonSerializable
         return self::$openAPIFormats;
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables;
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -176,7 +234,25 @@ class DogAllOf implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function __construct(array $data = null)
     {
-        $this->container['breed'] = $data['breed'] ?? null;
+        $this->setIfExists('breed', $data ?? [], null);
+    }
+
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
     }
 
     /**
@@ -222,6 +298,11 @@ class DogAllOf implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setBreed($breed)
     {
+
+        if (is_null($breed)) {
+            throw new \InvalidArgumentException('non-nullable breed cannot be null');
+        }
+
         $this->container['breed'] = $breed;
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/EnumArrays.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/EnumArrays.php
index a967b35062e..17f2a709521 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/EnumArrays.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/EnumArrays.php
@@ -73,6 +73,23 @@ class EnumArrays implements ModelInterface, ArrayAccess, \JsonSerializable
         'array_enum' => null
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        'just_symbol' => false,
+		'array_enum' => false
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -93,6 +110,48 @@ class EnumArrays implements ModelInterface, ArrayAccess, \JsonSerializable
         return self::$openAPIFormats;
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables;
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -211,8 +270,26 @@ class EnumArrays implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function __construct(array $data = null)
     {
-        $this->container['just_symbol'] = $data['just_symbol'] ?? null;
-        $this->container['array_enum'] = $data['array_enum'] ?? null;
+        $this->setIfExists('just_symbol', $data ?? [], null);
+        $this->setIfExists('array_enum', $data ?? [], null);
+    }
+
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
     }
 
     /**
@@ -277,6 +354,11 @@ class EnumArrays implements ModelInterface, ArrayAccess, \JsonSerializable
                 )
             );
         }
+
+        if (is_null($just_symbol)) {
+            throw new \InvalidArgumentException('non-nullable just_symbol cannot be null');
+        }
+
         $this->container['just_symbol'] = $just_symbol;
 
         return $this;
@@ -310,6 +392,11 @@ class EnumArrays implements ModelInterface, ArrayAccess, \JsonSerializable
                 )
             );
         }
+
+        if (is_null($array_enum)) {
+            throw new \InvalidArgumentException('non-nullable array_enum cannot be null');
+        }
+
         $this->container['array_enum'] = $array_enum;
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/EnumTest.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/EnumTest.php
index b390c6c3445..8d542cc3b12 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/EnumTest.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/EnumTest.php
@@ -85,6 +85,29 @@ class EnumTest implements ModelInterface, ArrayAccess, \JsonSerializable
         'outer_enum_integer_default_value' => null
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        'enum_string' => false,
+		'enum_string_required' => false,
+		'enum_integer' => false,
+		'enum_number' => false,
+		'outer_enum' => true,
+		'outer_enum_integer' => false,
+		'outer_enum_default_value' => false,
+		'outer_enum_integer_default_value' => false
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -105,6 +128,48 @@ class EnumTest implements ModelInterface, ArrayAccess, \JsonSerializable
         return self::$openAPIFormats;
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables;
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -275,14 +340,32 @@ class EnumTest implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function __construct(array $data = null)
     {
-        $this->container['enum_string'] = $data['enum_string'] ?? null;
-        $this->container['enum_string_required'] = $data['enum_string_required'] ?? null;
-        $this->container['enum_integer'] = $data['enum_integer'] ?? null;
-        $this->container['enum_number'] = $data['enum_number'] ?? null;
-        $this->container['outer_enum'] = $data['outer_enum'] ?? null;
-        $this->container['outer_enum_integer'] = $data['outer_enum_integer'] ?? null;
-        $this->container['outer_enum_default_value'] = $data['outer_enum_default_value'] ?? null;
-        $this->container['outer_enum_integer_default_value'] = $data['outer_enum_integer_default_value'] ?? null;
+        $this->setIfExists('enum_string', $data ?? [], null);
+        $this->setIfExists('enum_string_required', $data ?? [], null);
+        $this->setIfExists('enum_integer', $data ?? [], null);
+        $this->setIfExists('enum_number', $data ?? [], null);
+        $this->setIfExists('outer_enum', $data ?? [], null);
+        $this->setIfExists('outer_enum_integer', $data ?? [], null);
+        $this->setIfExists('outer_enum_default_value', $data ?? [], null);
+        $this->setIfExists('outer_enum_integer_default_value', $data ?? [], null);
+    }
+
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
     }
 
     /**
@@ -377,6 +460,11 @@ class EnumTest implements ModelInterface, ArrayAccess, \JsonSerializable
                 )
             );
         }
+
+        if (is_null($enum_string)) {
+            throw new \InvalidArgumentException('non-nullable enum_string cannot be null');
+        }
+
         $this->container['enum_string'] = $enum_string;
 
         return $this;
@@ -411,6 +499,11 @@ class EnumTest implements ModelInterface, ArrayAccess, \JsonSerializable
                 )
             );
         }
+
+        if (is_null($enum_string_required)) {
+            throw new \InvalidArgumentException('non-nullable enum_string_required cannot be null');
+        }
+
         $this->container['enum_string_required'] = $enum_string_required;
 
         return $this;
@@ -445,6 +538,11 @@ class EnumTest implements ModelInterface, ArrayAccess, \JsonSerializable
                 )
             );
         }
+
+        if (is_null($enum_integer)) {
+            throw new \InvalidArgumentException('non-nullable enum_integer cannot be null');
+        }
+
         $this->container['enum_integer'] = $enum_integer;
 
         return $this;
@@ -479,6 +577,11 @@ class EnumTest implements ModelInterface, ArrayAccess, \JsonSerializable
                 )
             );
         }
+
+        if (is_null($enum_number)) {
+            throw new \InvalidArgumentException('non-nullable enum_number cannot be null');
+        }
+
         $this->container['enum_number'] = $enum_number;
 
         return $this;
@@ -503,6 +606,18 @@ class EnumTest implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setOuterEnum($outer_enum)
     {
+
+        if (is_null($outer_enum)) {
+            array_push($this->openAPINullablesSetToNull, 'outer_enum');
+        } else {
+            $nullablesSetToNull = $this->getOpenAPINullablesSetToNull();
+            $index = array_search('outer_enum', $nullablesSetToNull);
+            if ($index !== FALSE) {
+                unset($nullablesSetToNull[$index]);
+                $this->setOpenAPINullablesSetToNull($nullablesSetToNull);
+            }
+        }
+
         $this->container['outer_enum'] = $outer_enum;
 
         return $this;
@@ -527,6 +642,11 @@ class EnumTest implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setOuterEnumInteger($outer_enum_integer)
     {
+
+        if (is_null($outer_enum_integer)) {
+            throw new \InvalidArgumentException('non-nullable outer_enum_integer cannot be null');
+        }
+
         $this->container['outer_enum_integer'] = $outer_enum_integer;
 
         return $this;
@@ -551,6 +671,11 @@ class EnumTest implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setOuterEnumDefaultValue($outer_enum_default_value)
     {
+
+        if (is_null($outer_enum_default_value)) {
+            throw new \InvalidArgumentException('non-nullable outer_enum_default_value cannot be null');
+        }
+
         $this->container['outer_enum_default_value'] = $outer_enum_default_value;
 
         return $this;
@@ -575,6 +700,11 @@ class EnumTest implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setOuterEnumIntegerDefaultValue($outer_enum_integer_default_value)
     {
+
+        if (is_null($outer_enum_integer_default_value)) {
+            throw new \InvalidArgumentException('non-nullable outer_enum_integer_default_value cannot be null');
+        }
+
         $this->container['outer_enum_integer_default_value'] = $outer_enum_integer_default_value;
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/File.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/File.php
index 683b7cba3ec..4a393a7c8b1 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/File.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/File.php
@@ -72,6 +72,22 @@ class File implements ModelInterface, ArrayAccess, \JsonSerializable
         'source_uri' => null
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        'source_uri' => false
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -92,6 +108,48 @@ class File implements ModelInterface, ArrayAccess, \JsonSerializable
         return self::$openAPIFormats;
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables;
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -177,7 +235,25 @@ class File implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function __construct(array $data = null)
     {
-        $this->container['source_uri'] = $data['source_uri'] ?? null;
+        $this->setIfExists('source_uri', $data ?? [], null);
+    }
+
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
     }
 
     /**
@@ -223,6 +299,11 @@ class File implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setSourceUri($source_uri)
     {
+
+        if (is_null($source_uri)) {
+            throw new \InvalidArgumentException('non-nullable source_uri cannot be null');
+        }
+
         $this->container['source_uri'] = $source_uri;
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/FileSchemaTestClass.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/FileSchemaTestClass.php
index 8a4e0547a09..f9382d5b073 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/FileSchemaTestClass.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/FileSchemaTestClass.php
@@ -73,6 +73,23 @@ class FileSchemaTestClass implements ModelInterface, ArrayAccess, \JsonSerializa
         'files' => null
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        'file' => false,
+		'files' => false
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -93,6 +110,48 @@ class FileSchemaTestClass implements ModelInterface, ArrayAccess, \JsonSerializa
         return self::$openAPIFormats;
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables;
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -181,8 +240,26 @@ class FileSchemaTestClass implements ModelInterface, ArrayAccess, \JsonSerializa
      */
     public function __construct(array $data = null)
     {
-        $this->container['file'] = $data['file'] ?? null;
-        $this->container['files'] = $data['files'] ?? null;
+        $this->setIfExists('file', $data ?? [], null);
+        $this->setIfExists('files', $data ?? [], null);
+    }
+
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
     }
 
     /**
@@ -228,6 +305,11 @@ class FileSchemaTestClass implements ModelInterface, ArrayAccess, \JsonSerializa
      */
     public function setFile($file)
     {
+
+        if (is_null($file)) {
+            throw new \InvalidArgumentException('non-nullable file cannot be null');
+        }
+
         $this->container['file'] = $file;
 
         return $this;
@@ -252,6 +334,11 @@ class FileSchemaTestClass implements ModelInterface, ArrayAccess, \JsonSerializa
      */
     public function setFiles($files)
     {
+
+        if (is_null($files)) {
+            throw new \InvalidArgumentException('non-nullable files cannot be null');
+        }
+
         $this->container['files'] = $files;
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Foo.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Foo.php
index 7fd28d1d32b..61d66a1e888 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Foo.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Foo.php
@@ -71,6 +71,22 @@ class Foo implements ModelInterface, ArrayAccess, \JsonSerializable
         'bar' => null
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        'bar' => false
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -91,6 +107,48 @@ class Foo implements ModelInterface, ArrayAccess, \JsonSerializable
         return self::$openAPIFormats;
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables;
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -176,7 +234,25 @@ class Foo implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function __construct(array $data = null)
     {
-        $this->container['bar'] = $data['bar'] ?? 'bar';
+        $this->setIfExists('bar', $data ?? [], 'bar');
+    }
+
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
     }
 
     /**
@@ -222,6 +298,11 @@ class Foo implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setBar($bar)
     {
+
+        if (is_null($bar)) {
+            throw new \InvalidArgumentException('non-nullable bar cannot be null');
+        }
+
         $this->container['bar'] = $bar;
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/FooGetDefaultResponse.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/FooGetDefaultResponse.php
index b012ce059a5..10e24c1300f 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/FooGetDefaultResponse.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/FooGetDefaultResponse.php
@@ -71,6 +71,22 @@ class FooGetDefaultResponse implements ModelInterface, ArrayAccess, \JsonSeriali
         'string' => null
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        'string' => false
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -91,6 +107,48 @@ class FooGetDefaultResponse implements ModelInterface, ArrayAccess, \JsonSeriali
         return self::$openAPIFormats;
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables;
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -176,7 +234,25 @@ class FooGetDefaultResponse implements ModelInterface, ArrayAccess, \JsonSeriali
      */
     public function __construct(array $data = null)
     {
-        $this->container['string'] = $data['string'] ?? null;
+        $this->setIfExists('string', $data ?? [], null);
+    }
+
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
     }
 
     /**
@@ -222,6 +298,11 @@ class FooGetDefaultResponse implements ModelInterface, ArrayAccess, \JsonSeriali
      */
     public function setString($string)
     {
+
+        if (is_null($string)) {
+            throw new \InvalidArgumentException('non-nullable string cannot be null');
+        }
+
         $this->container['string'] = $string;
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/FormatTest.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/FormatTest.php
index 78f7dc8cce0..1e8655a6aa4 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/FormatTest.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/FormatTest.php
@@ -101,6 +101,37 @@ class FormatTest implements ModelInterface, ArrayAccess, \JsonSerializable
         'pattern_with_digits_and_delimiter' => null
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        'integer' => false,
+		'int32' => false,
+		'int64' => false,
+		'number' => false,
+		'float' => false,
+		'double' => false,
+		'decimal' => false,
+		'string' => false,
+		'byte' => false,
+		'binary' => false,
+		'date' => false,
+		'date_time' => false,
+		'uuid' => false,
+		'password' => false,
+		'pattern_with_digits' => false,
+		'pattern_with_digits_and_delimiter' => false
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -121,6 +152,48 @@ class FormatTest implements ModelInterface, ArrayAccess, \JsonSerializable
         return self::$openAPIFormats;
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables;
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -251,22 +324,40 @@ class FormatTest implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function __construct(array $data = null)
     {
-        $this->container['integer'] = $data['integer'] ?? null;
-        $this->container['int32'] = $data['int32'] ?? null;
-        $this->container['int64'] = $data['int64'] ?? null;
-        $this->container['number'] = $data['number'] ?? null;
-        $this->container['float'] = $data['float'] ?? null;
-        $this->container['double'] = $data['double'] ?? null;
-        $this->container['decimal'] = $data['decimal'] ?? null;
-        $this->container['string'] = $data['string'] ?? null;
-        $this->container['byte'] = $data['byte'] ?? null;
-        $this->container['binary'] = $data['binary'] ?? null;
-        $this->container['date'] = $data['date'] ?? null;
-        $this->container['date_time'] = $data['date_time'] ?? null;
-        $this->container['uuid'] = $data['uuid'] ?? null;
-        $this->container['password'] = $data['password'] ?? null;
-        $this->container['pattern_with_digits'] = $data['pattern_with_digits'] ?? null;
-        $this->container['pattern_with_digits_and_delimiter'] = $data['pattern_with_digits_and_delimiter'] ?? null;
+        $this->setIfExists('integer', $data ?? [], null);
+        $this->setIfExists('int32', $data ?? [], null);
+        $this->setIfExists('int64', $data ?? [], null);
+        $this->setIfExists('number', $data ?? [], null);
+        $this->setIfExists('float', $data ?? [], null);
+        $this->setIfExists('double', $data ?? [], null);
+        $this->setIfExists('decimal', $data ?? [], null);
+        $this->setIfExists('string', $data ?? [], null);
+        $this->setIfExists('byte', $data ?? [], null);
+        $this->setIfExists('binary', $data ?? [], null);
+        $this->setIfExists('date', $data ?? [], null);
+        $this->setIfExists('date_time', $data ?? [], null);
+        $this->setIfExists('uuid', $data ?? [], null);
+        $this->setIfExists('password', $data ?? [], null);
+        $this->setIfExists('pattern_with_digits', $data ?? [], null);
+        $this->setIfExists('pattern_with_digits_and_delimiter', $data ?? [], null);
+    }
+
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
     }
 
     /**
@@ -392,6 +483,11 @@ class FormatTest implements ModelInterface, ArrayAccess, \JsonSerializable
             throw new \InvalidArgumentException('invalid value for $integer when calling FormatTest., must be bigger than or equal to 10.');
         }
 
+
+        if (is_null($integer)) {
+            throw new \InvalidArgumentException('non-nullable integer cannot be null');
+        }
+
         $this->container['integer'] = $integer;
 
         return $this;
@@ -424,6 +520,11 @@ class FormatTest implements ModelInterface, ArrayAccess, \JsonSerializable
             throw new \InvalidArgumentException('invalid value for $int32 when calling FormatTest., must be bigger than or equal to 20.');
         }
 
+
+        if (is_null($int32)) {
+            throw new \InvalidArgumentException('non-nullable int32 cannot be null');
+        }
+
         $this->container['int32'] = $int32;
 
         return $this;
@@ -448,6 +549,11 @@ class FormatTest implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setInt64($int64)
     {
+
+        if (is_null($int64)) {
+            throw new \InvalidArgumentException('non-nullable int64 cannot be null');
+        }
+
         $this->container['int64'] = $int64;
 
         return $this;
@@ -480,6 +586,11 @@ class FormatTest implements ModelInterface, ArrayAccess, \JsonSerializable
             throw new \InvalidArgumentException('invalid value for $number when calling FormatTest., must be bigger than or equal to 32.1.');
         }
 
+
+        if (is_null($number)) {
+            throw new \InvalidArgumentException('non-nullable number cannot be null');
+        }
+
         $this->container['number'] = $number;
 
         return $this;
@@ -512,6 +623,11 @@ class FormatTest implements ModelInterface, ArrayAccess, \JsonSerializable
             throw new \InvalidArgumentException('invalid value for $float when calling FormatTest., must be bigger than or equal to 54.3.');
         }
 
+
+        if (is_null($float)) {
+            throw new \InvalidArgumentException('non-nullable float cannot be null');
+        }
+
         $this->container['float'] = $float;
 
         return $this;
@@ -544,6 +660,11 @@ class FormatTest implements ModelInterface, ArrayAccess, \JsonSerializable
             throw new \InvalidArgumentException('invalid value for $double when calling FormatTest., must be bigger than or equal to 67.8.');
         }
 
+
+        if (is_null($double)) {
+            throw new \InvalidArgumentException('non-nullable double cannot be null');
+        }
+
         $this->container['double'] = $double;
 
         return $this;
@@ -568,6 +689,11 @@ class FormatTest implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setDecimal($decimal)
     {
+
+        if (is_null($decimal)) {
+            throw new \InvalidArgumentException('non-nullable decimal cannot be null');
+        }
+
         $this->container['decimal'] = $decimal;
 
         return $this;
@@ -597,6 +723,11 @@ class FormatTest implements ModelInterface, ArrayAccess, \JsonSerializable
             throw new \InvalidArgumentException("invalid value for \$string when calling FormatTest., must conform to the pattern /[a-z]/i.");
         }
 
+
+        if (is_null($string)) {
+            throw new \InvalidArgumentException('non-nullable string cannot be null');
+        }
+
         $this->container['string'] = $string;
 
         return $this;
@@ -621,6 +752,11 @@ class FormatTest implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setByte($byte)
     {
+
+        if (is_null($byte)) {
+            throw new \InvalidArgumentException('non-nullable byte cannot be null');
+        }
+
         $this->container['byte'] = $byte;
 
         return $this;
@@ -645,6 +781,11 @@ class FormatTest implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setBinary($binary)
     {
+
+        if (is_null($binary)) {
+            throw new \InvalidArgumentException('non-nullable binary cannot be null');
+        }
+
         $this->container['binary'] = $binary;
 
         return $this;
@@ -669,6 +810,11 @@ class FormatTest implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setDate($date)
     {
+
+        if (is_null($date)) {
+            throw new \InvalidArgumentException('non-nullable date cannot be null');
+        }
+
         $this->container['date'] = $date;
 
         return $this;
@@ -693,6 +839,11 @@ class FormatTest implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setDateTime($date_time)
     {
+
+        if (is_null($date_time)) {
+            throw new \InvalidArgumentException('non-nullable date_time cannot be null');
+        }
+
         $this->container['date_time'] = $date_time;
 
         return $this;
@@ -717,6 +868,11 @@ class FormatTest implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setUuid($uuid)
     {
+
+        if (is_null($uuid)) {
+            throw new \InvalidArgumentException('non-nullable uuid cannot be null');
+        }
+
         $this->container['uuid'] = $uuid;
 
         return $this;
@@ -748,6 +904,11 @@ class FormatTest implements ModelInterface, ArrayAccess, \JsonSerializable
             throw new \InvalidArgumentException('invalid length for $password when calling FormatTest., must be bigger than or equal to 10.');
         }
 
+
+        if (is_null($password)) {
+            throw new \InvalidArgumentException('non-nullable password cannot be null');
+        }
+
         $this->container['password'] = $password;
 
         return $this;
@@ -777,6 +938,11 @@ class FormatTest implements ModelInterface, ArrayAccess, \JsonSerializable
             throw new \InvalidArgumentException("invalid value for \$pattern_with_digits when calling FormatTest., must conform to the pattern /^\\d{10}$/.");
         }
 
+
+        if (is_null($pattern_with_digits)) {
+            throw new \InvalidArgumentException('non-nullable pattern_with_digits cannot be null');
+        }
+
         $this->container['pattern_with_digits'] = $pattern_with_digits;
 
         return $this;
@@ -806,6 +972,11 @@ class FormatTest implements ModelInterface, ArrayAccess, \JsonSerializable
             throw new \InvalidArgumentException("invalid value for \$pattern_with_digits_and_delimiter when calling FormatTest., must conform to the pattern /^image_\\d{1,3}$/i.");
         }
 
+
+        if (is_null($pattern_with_digits_and_delimiter)) {
+            throw new \InvalidArgumentException('non-nullable pattern_with_digits_and_delimiter cannot be null');
+        }
+
         $this->container['pattern_with_digits_and_delimiter'] = $pattern_with_digits_and_delimiter;
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/HasOnlyReadOnly.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/HasOnlyReadOnly.php
index acb291c965a..5eeb4f7cc25 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/HasOnlyReadOnly.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/HasOnlyReadOnly.php
@@ -73,6 +73,23 @@ class HasOnlyReadOnly implements ModelInterface, ArrayAccess, \JsonSerializable
         'foo' => null
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        'bar' => false,
+		'foo' => false
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -93,6 +110,48 @@ class HasOnlyReadOnly implements ModelInterface, ArrayAccess, \JsonSerializable
         return self::$openAPIFormats;
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables;
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -181,8 +240,26 @@ class HasOnlyReadOnly implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function __construct(array $data = null)
     {
-        $this->container['bar'] = $data['bar'] ?? null;
-        $this->container['foo'] = $data['foo'] ?? null;
+        $this->setIfExists('bar', $data ?? [], null);
+        $this->setIfExists('foo', $data ?? [], null);
+    }
+
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
     }
 
     /**
@@ -228,6 +305,11 @@ class HasOnlyReadOnly implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setBar($bar)
     {
+
+        if (is_null($bar)) {
+            throw new \InvalidArgumentException('non-nullable bar cannot be null');
+        }
+
         $this->container['bar'] = $bar;
 
         return $this;
@@ -252,6 +334,11 @@ class HasOnlyReadOnly implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setFoo($foo)
     {
+
+        if (is_null($foo)) {
+            throw new \InvalidArgumentException('non-nullable foo cannot be null');
+        }
+
         $this->container['foo'] = $foo;
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/HealthCheckResult.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/HealthCheckResult.php
index 04d9fef0e76..55e483dab50 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/HealthCheckResult.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/HealthCheckResult.php
@@ -72,6 +72,22 @@ class HealthCheckResult implements ModelInterface, ArrayAccess, \JsonSerializabl
         'nullable_message' => null
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        'nullable_message' => true
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -92,6 +108,48 @@ class HealthCheckResult implements ModelInterface, ArrayAccess, \JsonSerializabl
         return self::$openAPIFormats;
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables;
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -177,7 +235,25 @@ class HealthCheckResult implements ModelInterface, ArrayAccess, \JsonSerializabl
      */
     public function __construct(array $data = null)
     {
-        $this->container['nullable_message'] = $data['nullable_message'] ?? null;
+        $this->setIfExists('nullable_message', $data ?? [], null);
+    }
+
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
     }
 
     /**
@@ -223,6 +299,18 @@ class HealthCheckResult implements ModelInterface, ArrayAccess, \JsonSerializabl
      */
     public function setNullableMessage($nullable_message)
     {
+
+        if (is_null($nullable_message)) {
+            array_push($this->openAPINullablesSetToNull, 'nullable_message');
+        } else {
+            $nullablesSetToNull = $this->getOpenAPINullablesSetToNull();
+            $index = array_search('nullable_message', $nullablesSetToNull);
+            if ($index !== FALSE) {
+                unset($nullablesSetToNull[$index]);
+                $this->setOpenAPINullablesSetToNull($nullablesSetToNull);
+            }
+        }
+
         $this->container['nullable_message'] = $nullable_message;
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/MapTest.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/MapTest.php
index 1b88cd50bef..899e4a5bb96 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/MapTest.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/MapTest.php
@@ -77,6 +77,25 @@ class MapTest implements ModelInterface, ArrayAccess, \JsonSerializable
         'indirect_map' => null
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        'map_map_of_string' => false,
+		'map_of_enum_string' => false,
+		'direct_map' => false,
+		'indirect_map' => false
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -97,6 +116,48 @@ class MapTest implements ModelInterface, ArrayAccess, \JsonSerializable
         return self::$openAPIFormats;
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables;
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -206,10 +267,28 @@ class MapTest implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function __construct(array $data = null)
     {
-        $this->container['map_map_of_string'] = $data['map_map_of_string'] ?? null;
-        $this->container['map_of_enum_string'] = $data['map_of_enum_string'] ?? null;
-        $this->container['direct_map'] = $data['direct_map'] ?? null;
-        $this->container['indirect_map'] = $data['indirect_map'] ?? null;
+        $this->setIfExists('map_map_of_string', $data ?? [], null);
+        $this->setIfExists('map_of_enum_string', $data ?? [], null);
+        $this->setIfExists('direct_map', $data ?? [], null);
+        $this->setIfExists('indirect_map', $data ?? [], null);
+    }
+
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
     }
 
     /**
@@ -255,6 +334,11 @@ class MapTest implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setMapMapOfString($map_map_of_string)
     {
+
+        if (is_null($map_map_of_string)) {
+            throw new \InvalidArgumentException('non-nullable map_map_of_string cannot be null');
+        }
+
         $this->container['map_map_of_string'] = $map_map_of_string;
 
         return $this;
@@ -288,6 +372,11 @@ class MapTest implements ModelInterface, ArrayAccess, \JsonSerializable
                 )
             );
         }
+
+        if (is_null($map_of_enum_string)) {
+            throw new \InvalidArgumentException('non-nullable map_of_enum_string cannot be null');
+        }
+
         $this->container['map_of_enum_string'] = $map_of_enum_string;
 
         return $this;
@@ -312,6 +401,11 @@ class MapTest implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setDirectMap($direct_map)
     {
+
+        if (is_null($direct_map)) {
+            throw new \InvalidArgumentException('non-nullable direct_map cannot be null');
+        }
+
         $this->container['direct_map'] = $direct_map;
 
         return $this;
@@ -336,6 +430,11 @@ class MapTest implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setIndirectMap($indirect_map)
     {
+
+        if (is_null($indirect_map)) {
+            throw new \InvalidArgumentException('non-nullable indirect_map cannot be null');
+        }
+
         $this->container['indirect_map'] = $indirect_map;
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/MixedPropertiesAndAdditionalPropertiesClass.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/MixedPropertiesAndAdditionalPropertiesClass.php
index d9d49796a72..9c104a61118 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/MixedPropertiesAndAdditionalPropertiesClass.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/MixedPropertiesAndAdditionalPropertiesClass.php
@@ -75,6 +75,24 @@ class MixedPropertiesAndAdditionalPropertiesClass implements ModelInterface, Arr
         'map' => null
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        'uuid' => false,
+		'date_time' => false,
+		'map' => false
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -95,6 +113,48 @@ class MixedPropertiesAndAdditionalPropertiesClass implements ModelInterface, Arr
         return self::$openAPIFormats;
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables;
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -186,9 +246,27 @@ class MixedPropertiesAndAdditionalPropertiesClass implements ModelInterface, Arr
      */
     public function __construct(array $data = null)
     {
-        $this->container['uuid'] = $data['uuid'] ?? null;
-        $this->container['date_time'] = $data['date_time'] ?? null;
-        $this->container['map'] = $data['map'] ?? null;
+        $this->setIfExists('uuid', $data ?? [], null);
+        $this->setIfExists('date_time', $data ?? [], null);
+        $this->setIfExists('map', $data ?? [], null);
+    }
+
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
     }
 
     /**
@@ -234,6 +312,11 @@ class MixedPropertiesAndAdditionalPropertiesClass implements ModelInterface, Arr
      */
     public function setUuid($uuid)
     {
+
+        if (is_null($uuid)) {
+            throw new \InvalidArgumentException('non-nullable uuid cannot be null');
+        }
+
         $this->container['uuid'] = $uuid;
 
         return $this;
@@ -258,6 +341,11 @@ class MixedPropertiesAndAdditionalPropertiesClass implements ModelInterface, Arr
      */
     public function setDateTime($date_time)
     {
+
+        if (is_null($date_time)) {
+            throw new \InvalidArgumentException('non-nullable date_time cannot be null');
+        }
+
         $this->container['date_time'] = $date_time;
 
         return $this;
@@ -282,6 +370,11 @@ class MixedPropertiesAndAdditionalPropertiesClass implements ModelInterface, Arr
      */
     public function setMap($map)
     {
+
+        if (is_null($map)) {
+            throw new \InvalidArgumentException('non-nullable map cannot be null');
+        }
+
         $this->container['map'] = $map;
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Model200Response.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Model200Response.php
index 37cd9b17f4d..232a99d6167 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Model200Response.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Model200Response.php
@@ -74,6 +74,23 @@ class Model200Response implements ModelInterface, ArrayAccess, \JsonSerializable
         'class' => null
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        'name' => false,
+		'class' => false
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -94,6 +111,48 @@ class Model200Response implements ModelInterface, ArrayAccess, \JsonSerializable
         return self::$openAPIFormats;
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables;
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -182,8 +241,26 @@ class Model200Response implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function __construct(array $data = null)
     {
-        $this->container['name'] = $data['name'] ?? null;
-        $this->container['class'] = $data['class'] ?? null;
+        $this->setIfExists('name', $data ?? [], null);
+        $this->setIfExists('class', $data ?? [], null);
+    }
+
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
     }
 
     /**
@@ -229,6 +306,11 @@ class Model200Response implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setName($name)
     {
+
+        if (is_null($name)) {
+            throw new \InvalidArgumentException('non-nullable name cannot be null');
+        }
+
         $this->container['name'] = $name;
 
         return $this;
@@ -253,6 +335,11 @@ class Model200Response implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setClass($class)
     {
+
+        if (is_null($class)) {
+            throw new \InvalidArgumentException('non-nullable class cannot be null');
+        }
+
         $this->container['class'] = $class;
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ModelInterface.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ModelInterface.php
index 935d8833fd4..ccd87eb6104 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ModelInterface.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ModelInterface.php
@@ -92,4 +92,20 @@ interface ModelInterface
      * @return bool
      */
     public function valid();
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool;
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool;
 }
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ModelList.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ModelList.php
index 42e7e3e3d78..f921a0ba525 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ModelList.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ModelList.php
@@ -71,6 +71,22 @@ class ModelList implements ModelInterface, ArrayAccess, \JsonSerializable
         '_123_list' => null
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        '_123_list' => false
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -91,6 +107,48 @@ class ModelList implements ModelInterface, ArrayAccess, \JsonSerializable
         return self::$openAPIFormats;
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables;
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -176,7 +234,25 @@ class ModelList implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function __construct(array $data = null)
     {
-        $this->container['_123_list'] = $data['_123_list'] ?? null;
+        $this->setIfExists('_123_list', $data ?? [], null);
+    }
+
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
     }
 
     /**
@@ -222,6 +298,11 @@ class ModelList implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function set123List($_123_list)
     {
+
+        if (is_null($_123_list)) {
+            throw new \InvalidArgumentException('non-nullable _123_list cannot be null');
+        }
+
         $this->container['_123_list'] = $_123_list;
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ModelReturn.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ModelReturn.php
index 3593ce0ed60..c9695f24101 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ModelReturn.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ModelReturn.php
@@ -72,6 +72,22 @@ class ModelReturn implements ModelInterface, ArrayAccess, \JsonSerializable
         'return' => 'int32'
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        'return' => false
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -92,6 +108,48 @@ class ModelReturn implements ModelInterface, ArrayAccess, \JsonSerializable
         return self::$openAPIFormats;
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables;
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -177,7 +235,25 @@ class ModelReturn implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function __construct(array $data = null)
     {
-        $this->container['return'] = $data['return'] ?? null;
+        $this->setIfExists('return', $data ?? [], null);
+    }
+
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
     }
 
     /**
@@ -223,6 +299,11 @@ class ModelReturn implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setReturn($return)
     {
+
+        if (is_null($return)) {
+            throw new \InvalidArgumentException('non-nullable return cannot be null');
+        }
+
         $this->container['return'] = $return;
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Name.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Name.php
index 5a62ac60cbe..01605009e7b 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Name.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Name.php
@@ -78,6 +78,25 @@ class Name implements ModelInterface, ArrayAccess, \JsonSerializable
         '_123_number' => null
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        'name' => false,
+		'snake_case' => false,
+		'property' => false,
+		'_123_number' => false
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -98,6 +117,48 @@ class Name implements ModelInterface, ArrayAccess, \JsonSerializable
         return self::$openAPIFormats;
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables;
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -192,10 +253,28 @@ class Name implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function __construct(array $data = null)
     {
-        $this->container['name'] = $data['name'] ?? null;
-        $this->container['snake_case'] = $data['snake_case'] ?? null;
-        $this->container['property'] = $data['property'] ?? null;
-        $this->container['_123_number'] = $data['_123_number'] ?? null;
+        $this->setIfExists('name', $data ?? [], null);
+        $this->setIfExists('snake_case', $data ?? [], null);
+        $this->setIfExists('property', $data ?? [], null);
+        $this->setIfExists('_123_number', $data ?? [], null);
+    }
+
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
     }
 
     /**
@@ -244,6 +323,11 @@ class Name implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setName($name)
     {
+
+        if (is_null($name)) {
+            throw new \InvalidArgumentException('non-nullable name cannot be null');
+        }
+
         $this->container['name'] = $name;
 
         return $this;
@@ -268,6 +352,11 @@ class Name implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setSnakeCase($snake_case)
     {
+
+        if (is_null($snake_case)) {
+            throw new \InvalidArgumentException('non-nullable snake_case cannot be null');
+        }
+
         $this->container['snake_case'] = $snake_case;
 
         return $this;
@@ -292,6 +381,11 @@ class Name implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setProperty($property)
     {
+
+        if (is_null($property)) {
+            throw new \InvalidArgumentException('non-nullable property cannot be null');
+        }
+
         $this->container['property'] = $property;
 
         return $this;
@@ -316,6 +410,11 @@ class Name implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function set123Number($_123_number)
     {
+
+        if (is_null($_123_number)) {
+            throw new \InvalidArgumentException('non-nullable _123_number cannot be null');
+        }
+
         $this->container['_123_number'] = $_123_number;
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/NullableClass.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/NullableClass.php
index 4bb135c4d52..c5f3e7a12fc 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/NullableClass.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/NullableClass.php
@@ -93,6 +93,33 @@ class NullableClass implements ModelInterface, ArrayAccess, \JsonSerializable
         'object_items_nullable' => null
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        'integer_prop' => true,
+		'number_prop' => true,
+		'boolean_prop' => true,
+		'string_prop' => true,
+		'date_prop' => true,
+		'datetime_prop' => true,
+		'array_nullable_prop' => true,
+		'array_and_items_nullable_prop' => true,
+		'array_items_nullable' => false,
+		'object_nullable_prop' => true,
+		'object_and_items_nullable_prop' => true,
+		'object_items_nullable' => false
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -113,6 +140,48 @@ class NullableClass implements ModelInterface, ArrayAccess, \JsonSerializable
         return self::$openAPIFormats;
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables;
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -231,18 +300,36 @@ class NullableClass implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function __construct(array $data = null)
     {
-        $this->container['integer_prop'] = $data['integer_prop'] ?? null;
-        $this->container['number_prop'] = $data['number_prop'] ?? null;
-        $this->container['boolean_prop'] = $data['boolean_prop'] ?? null;
-        $this->container['string_prop'] = $data['string_prop'] ?? null;
-        $this->container['date_prop'] = $data['date_prop'] ?? null;
-        $this->container['datetime_prop'] = $data['datetime_prop'] ?? null;
-        $this->container['array_nullable_prop'] = $data['array_nullable_prop'] ?? null;
-        $this->container['array_and_items_nullable_prop'] = $data['array_and_items_nullable_prop'] ?? null;
-        $this->container['array_items_nullable'] = $data['array_items_nullable'] ?? null;
-        $this->container['object_nullable_prop'] = $data['object_nullable_prop'] ?? null;
-        $this->container['object_and_items_nullable_prop'] = $data['object_and_items_nullable_prop'] ?? null;
-        $this->container['object_items_nullable'] = $data['object_items_nullable'] ?? null;
+        $this->setIfExists('integer_prop', $data ?? [], null);
+        $this->setIfExists('number_prop', $data ?? [], null);
+        $this->setIfExists('boolean_prop', $data ?? [], null);
+        $this->setIfExists('string_prop', $data ?? [], null);
+        $this->setIfExists('date_prop', $data ?? [], null);
+        $this->setIfExists('datetime_prop', $data ?? [], null);
+        $this->setIfExists('array_nullable_prop', $data ?? [], null);
+        $this->setIfExists('array_and_items_nullable_prop', $data ?? [], null);
+        $this->setIfExists('array_items_nullable', $data ?? [], null);
+        $this->setIfExists('object_nullable_prop', $data ?? [], null);
+        $this->setIfExists('object_and_items_nullable_prop', $data ?? [], null);
+        $this->setIfExists('object_items_nullable', $data ?? [], null);
+    }
+
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
     }
 
     /**
@@ -288,6 +375,18 @@ class NullableClass implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setIntegerProp($integer_prop)
     {
+
+        if (is_null($integer_prop)) {
+            array_push($this->openAPINullablesSetToNull, 'integer_prop');
+        } else {
+            $nullablesSetToNull = $this->getOpenAPINullablesSetToNull();
+            $index = array_search('integer_prop', $nullablesSetToNull);
+            if ($index !== FALSE) {
+                unset($nullablesSetToNull[$index]);
+                $this->setOpenAPINullablesSetToNull($nullablesSetToNull);
+            }
+        }
+
         $this->container['integer_prop'] = $integer_prop;
 
         return $this;
@@ -312,6 +411,18 @@ class NullableClass implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setNumberProp($number_prop)
     {
+
+        if (is_null($number_prop)) {
+            array_push($this->openAPINullablesSetToNull, 'number_prop');
+        } else {
+            $nullablesSetToNull = $this->getOpenAPINullablesSetToNull();
+            $index = array_search('number_prop', $nullablesSetToNull);
+            if ($index !== FALSE) {
+                unset($nullablesSetToNull[$index]);
+                $this->setOpenAPINullablesSetToNull($nullablesSetToNull);
+            }
+        }
+
         $this->container['number_prop'] = $number_prop;
 
         return $this;
@@ -336,6 +447,18 @@ class NullableClass implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setBooleanProp($boolean_prop)
     {
+
+        if (is_null($boolean_prop)) {
+            array_push($this->openAPINullablesSetToNull, 'boolean_prop');
+        } else {
+            $nullablesSetToNull = $this->getOpenAPINullablesSetToNull();
+            $index = array_search('boolean_prop', $nullablesSetToNull);
+            if ($index !== FALSE) {
+                unset($nullablesSetToNull[$index]);
+                $this->setOpenAPINullablesSetToNull($nullablesSetToNull);
+            }
+        }
+
         $this->container['boolean_prop'] = $boolean_prop;
 
         return $this;
@@ -360,6 +483,18 @@ class NullableClass implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setStringProp($string_prop)
     {
+
+        if (is_null($string_prop)) {
+            array_push($this->openAPINullablesSetToNull, 'string_prop');
+        } else {
+            $nullablesSetToNull = $this->getOpenAPINullablesSetToNull();
+            $index = array_search('string_prop', $nullablesSetToNull);
+            if ($index !== FALSE) {
+                unset($nullablesSetToNull[$index]);
+                $this->setOpenAPINullablesSetToNull($nullablesSetToNull);
+            }
+        }
+
         $this->container['string_prop'] = $string_prop;
 
         return $this;
@@ -384,6 +519,18 @@ class NullableClass implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setDateProp($date_prop)
     {
+
+        if (is_null($date_prop)) {
+            array_push($this->openAPINullablesSetToNull, 'date_prop');
+        } else {
+            $nullablesSetToNull = $this->getOpenAPINullablesSetToNull();
+            $index = array_search('date_prop', $nullablesSetToNull);
+            if ($index !== FALSE) {
+                unset($nullablesSetToNull[$index]);
+                $this->setOpenAPINullablesSetToNull($nullablesSetToNull);
+            }
+        }
+
         $this->container['date_prop'] = $date_prop;
 
         return $this;
@@ -408,6 +555,18 @@ class NullableClass implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setDatetimeProp($datetime_prop)
     {
+
+        if (is_null($datetime_prop)) {
+            array_push($this->openAPINullablesSetToNull, 'datetime_prop');
+        } else {
+            $nullablesSetToNull = $this->getOpenAPINullablesSetToNull();
+            $index = array_search('datetime_prop', $nullablesSetToNull);
+            if ($index !== FALSE) {
+                unset($nullablesSetToNull[$index]);
+                $this->setOpenAPINullablesSetToNull($nullablesSetToNull);
+            }
+        }
+
         $this->container['datetime_prop'] = $datetime_prop;
 
         return $this;
@@ -432,6 +591,18 @@ class NullableClass implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setArrayNullableProp($array_nullable_prop)
     {
+
+        if (is_null($array_nullable_prop)) {
+            array_push($this->openAPINullablesSetToNull, 'array_nullable_prop');
+        } else {
+            $nullablesSetToNull = $this->getOpenAPINullablesSetToNull();
+            $index = array_search('array_nullable_prop', $nullablesSetToNull);
+            if ($index !== FALSE) {
+                unset($nullablesSetToNull[$index]);
+                $this->setOpenAPINullablesSetToNull($nullablesSetToNull);
+            }
+        }
+
         $this->container['array_nullable_prop'] = $array_nullable_prop;
 
         return $this;
@@ -456,6 +627,18 @@ class NullableClass implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setArrayAndItemsNullableProp($array_and_items_nullable_prop)
     {
+
+        if (is_null($array_and_items_nullable_prop)) {
+            array_push($this->openAPINullablesSetToNull, 'array_and_items_nullable_prop');
+        } else {
+            $nullablesSetToNull = $this->getOpenAPINullablesSetToNull();
+            $index = array_search('array_and_items_nullable_prop', $nullablesSetToNull);
+            if ($index !== FALSE) {
+                unset($nullablesSetToNull[$index]);
+                $this->setOpenAPINullablesSetToNull($nullablesSetToNull);
+            }
+        }
+
         $this->container['array_and_items_nullable_prop'] = $array_and_items_nullable_prop;
 
         return $this;
@@ -480,6 +663,11 @@ class NullableClass implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setArrayItemsNullable($array_items_nullable)
     {
+
+        if (is_null($array_items_nullable)) {
+            throw new \InvalidArgumentException('non-nullable array_items_nullable cannot be null');
+        }
+
         $this->container['array_items_nullable'] = $array_items_nullable;
 
         return $this;
@@ -504,6 +692,18 @@ class NullableClass implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setObjectNullableProp($object_nullable_prop)
     {
+
+        if (is_null($object_nullable_prop)) {
+            array_push($this->openAPINullablesSetToNull, 'object_nullable_prop');
+        } else {
+            $nullablesSetToNull = $this->getOpenAPINullablesSetToNull();
+            $index = array_search('object_nullable_prop', $nullablesSetToNull);
+            if ($index !== FALSE) {
+                unset($nullablesSetToNull[$index]);
+                $this->setOpenAPINullablesSetToNull($nullablesSetToNull);
+            }
+        }
+
         $this->container['object_nullable_prop'] = $object_nullable_prop;
 
         return $this;
@@ -528,6 +728,18 @@ class NullableClass implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setObjectAndItemsNullableProp($object_and_items_nullable_prop)
     {
+
+        if (is_null($object_and_items_nullable_prop)) {
+            array_push($this->openAPINullablesSetToNull, 'object_and_items_nullable_prop');
+        } else {
+            $nullablesSetToNull = $this->getOpenAPINullablesSetToNull();
+            $index = array_search('object_and_items_nullable_prop', $nullablesSetToNull);
+            if ($index !== FALSE) {
+                unset($nullablesSetToNull[$index]);
+                $this->setOpenAPINullablesSetToNull($nullablesSetToNull);
+            }
+        }
+
         $this->container['object_and_items_nullable_prop'] = $object_and_items_nullable_prop;
 
         return $this;
@@ -552,6 +764,11 @@ class NullableClass implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setObjectItemsNullable($object_items_nullable)
     {
+
+        if (is_null($object_items_nullable)) {
+            throw new \InvalidArgumentException('non-nullable object_items_nullable cannot be null');
+        }
+
         $this->container['object_items_nullable'] = $object_items_nullable;
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/NumberOnly.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/NumberOnly.php
index 8ec732dd07c..43331582045 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/NumberOnly.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/NumberOnly.php
@@ -71,6 +71,22 @@ class NumberOnly implements ModelInterface, ArrayAccess, \JsonSerializable
         'just_number' => null
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        'just_number' => false
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -91,6 +107,48 @@ class NumberOnly implements ModelInterface, ArrayAccess, \JsonSerializable
         return self::$openAPIFormats;
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables;
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -176,7 +234,25 @@ class NumberOnly implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function __construct(array $data = null)
     {
-        $this->container['just_number'] = $data['just_number'] ?? null;
+        $this->setIfExists('just_number', $data ?? [], null);
+    }
+
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
     }
 
     /**
@@ -222,6 +298,11 @@ class NumberOnly implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setJustNumber($just_number)
     {
+
+        if (is_null($just_number)) {
+            throw new \InvalidArgumentException('non-nullable just_number cannot be null');
+        }
+
         $this->container['just_number'] = $just_number;
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ObjectWithDeprecatedFields.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ObjectWithDeprecatedFields.php
index c5f96667c19..26d50217665 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ObjectWithDeprecatedFields.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ObjectWithDeprecatedFields.php
@@ -77,6 +77,25 @@ class ObjectWithDeprecatedFields implements ModelInterface, ArrayAccess, \JsonSe
         'bars' => null
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        'uuid' => false,
+		'id' => false,
+		'deprecated_ref' => false,
+		'bars' => false
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -97,6 +116,48 @@ class ObjectWithDeprecatedFields implements ModelInterface, ArrayAccess, \JsonSe
         return self::$openAPIFormats;
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables;
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -191,10 +252,28 @@ class ObjectWithDeprecatedFields implements ModelInterface, ArrayAccess, \JsonSe
      */
     public function __construct(array $data = null)
     {
-        $this->container['uuid'] = $data['uuid'] ?? null;
-        $this->container['id'] = $data['id'] ?? null;
-        $this->container['deprecated_ref'] = $data['deprecated_ref'] ?? null;
-        $this->container['bars'] = $data['bars'] ?? null;
+        $this->setIfExists('uuid', $data ?? [], null);
+        $this->setIfExists('id', $data ?? [], null);
+        $this->setIfExists('deprecated_ref', $data ?? [], null);
+        $this->setIfExists('bars', $data ?? [], null);
+    }
+
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
     }
 
     /**
@@ -240,6 +319,11 @@ class ObjectWithDeprecatedFields implements ModelInterface, ArrayAccess, \JsonSe
      */
     public function setUuid($uuid)
     {
+
+        if (is_null($uuid)) {
+            throw new \InvalidArgumentException('non-nullable uuid cannot be null');
+        }
+
         $this->container['uuid'] = $uuid;
 
         return $this;
@@ -266,6 +350,11 @@ class ObjectWithDeprecatedFields implements ModelInterface, ArrayAccess, \JsonSe
      */
     public function setId($id)
     {
+
+        if (is_null($id)) {
+            throw new \InvalidArgumentException('non-nullable id cannot be null');
+        }
+
         $this->container['id'] = $id;
 
         return $this;
@@ -292,6 +381,11 @@ class ObjectWithDeprecatedFields implements ModelInterface, ArrayAccess, \JsonSe
      */
     public function setDeprecatedRef($deprecated_ref)
     {
+
+        if (is_null($deprecated_ref)) {
+            throw new \InvalidArgumentException('non-nullable deprecated_ref cannot be null');
+        }
+
         $this->container['deprecated_ref'] = $deprecated_ref;
 
         return $this;
@@ -318,6 +412,11 @@ class ObjectWithDeprecatedFields implements ModelInterface, ArrayAccess, \JsonSe
      */
     public function setBars($bars)
     {
+
+        if (is_null($bars)) {
+            throw new \InvalidArgumentException('non-nullable bars cannot be null');
+        }
+
         $this->container['bars'] = $bars;
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Order.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Order.php
index 87e8d176597..123766cea4b 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Order.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Order.php
@@ -81,6 +81,27 @@ class Order implements ModelInterface, ArrayAccess, \JsonSerializable
         'complete' => null
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        'id' => false,
+		'pet_id' => false,
+		'quantity' => false,
+		'ship_date' => false,
+		'status' => false,
+		'complete' => false
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -101,6 +122,48 @@ class Order implements ModelInterface, ArrayAccess, \JsonSerializable
         return self::$openAPIFormats;
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables;
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -218,12 +281,30 @@ class Order implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function __construct(array $data = null)
     {
-        $this->container['id'] = $data['id'] ?? null;
-        $this->container['pet_id'] = $data['pet_id'] ?? null;
-        $this->container['quantity'] = $data['quantity'] ?? null;
-        $this->container['ship_date'] = $data['ship_date'] ?? null;
-        $this->container['status'] = $data['status'] ?? null;
-        $this->container['complete'] = $data['complete'] ?? false;
+        $this->setIfExists('id', $data ?? [], null);
+        $this->setIfExists('pet_id', $data ?? [], null);
+        $this->setIfExists('quantity', $data ?? [], null);
+        $this->setIfExists('ship_date', $data ?? [], null);
+        $this->setIfExists('status', $data ?? [], null);
+        $this->setIfExists('complete', $data ?? [], false);
+    }
+
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
     }
 
     /**
@@ -278,6 +359,11 @@ class Order implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setId($id)
     {
+
+        if (is_null($id)) {
+            throw new \InvalidArgumentException('non-nullable id cannot be null');
+        }
+
         $this->container['id'] = $id;
 
         return $this;
@@ -302,6 +388,11 @@ class Order implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setPetId($pet_id)
     {
+
+        if (is_null($pet_id)) {
+            throw new \InvalidArgumentException('non-nullable pet_id cannot be null');
+        }
+
         $this->container['pet_id'] = $pet_id;
 
         return $this;
@@ -326,6 +417,11 @@ class Order implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setQuantity($quantity)
     {
+
+        if (is_null($quantity)) {
+            throw new \InvalidArgumentException('non-nullable quantity cannot be null');
+        }
+
         $this->container['quantity'] = $quantity;
 
         return $this;
@@ -350,6 +446,11 @@ class Order implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setShipDate($ship_date)
     {
+
+        if (is_null($ship_date)) {
+            throw new \InvalidArgumentException('non-nullable ship_date cannot be null');
+        }
+
         $this->container['ship_date'] = $ship_date;
 
         return $this;
@@ -384,6 +485,11 @@ class Order implements ModelInterface, ArrayAccess, \JsonSerializable
                 )
             );
         }
+
+        if (is_null($status)) {
+            throw new \InvalidArgumentException('non-nullable status cannot be null');
+        }
+
         $this->container['status'] = $status;
 
         return $this;
@@ -408,6 +514,11 @@ class Order implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setComplete($complete)
     {
+
+        if (is_null($complete)) {
+            throw new \InvalidArgumentException('non-nullable complete cannot be null');
+        }
+
         $this->container['complete'] = $complete;
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/OuterComposite.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/OuterComposite.php
index 76910f4e022..63f7a29b28b 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/OuterComposite.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/OuterComposite.php
@@ -75,6 +75,24 @@ class OuterComposite implements ModelInterface, ArrayAccess, \JsonSerializable
         'my_boolean' => null
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        'my_number' => false,
+		'my_string' => false,
+		'my_boolean' => false
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -95,6 +113,48 @@ class OuterComposite implements ModelInterface, ArrayAccess, \JsonSerializable
         return self::$openAPIFormats;
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables;
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -186,9 +246,27 @@ class OuterComposite implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function __construct(array $data = null)
     {
-        $this->container['my_number'] = $data['my_number'] ?? null;
-        $this->container['my_string'] = $data['my_string'] ?? null;
-        $this->container['my_boolean'] = $data['my_boolean'] ?? null;
+        $this->setIfExists('my_number', $data ?? [], null);
+        $this->setIfExists('my_string', $data ?? [], null);
+        $this->setIfExists('my_boolean', $data ?? [], null);
+    }
+
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
     }
 
     /**
@@ -234,6 +312,11 @@ class OuterComposite implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setMyNumber($my_number)
     {
+
+        if (is_null($my_number)) {
+            throw new \InvalidArgumentException('non-nullable my_number cannot be null');
+        }
+
         $this->container['my_number'] = $my_number;
 
         return $this;
@@ -258,6 +341,11 @@ class OuterComposite implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setMyString($my_string)
     {
+
+        if (is_null($my_string)) {
+            throw new \InvalidArgumentException('non-nullable my_string cannot be null');
+        }
+
         $this->container['my_string'] = $my_string;
 
         return $this;
@@ -282,6 +370,11 @@ class OuterComposite implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setMyBoolean($my_boolean)
     {
+
+        if (is_null($my_boolean)) {
+            throw new \InvalidArgumentException('non-nullable my_boolean cannot be null');
+        }
+
         $this->container['my_boolean'] = $my_boolean;
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/OuterObjectWithEnumProperty.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/OuterObjectWithEnumProperty.php
index 7e19b038a08..86ed80c8c1d 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/OuterObjectWithEnumProperty.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/OuterObjectWithEnumProperty.php
@@ -71,6 +71,22 @@ class OuterObjectWithEnumProperty implements ModelInterface, ArrayAccess, \JsonS
         'value' => null
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        'value' => false
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -91,6 +107,48 @@ class OuterObjectWithEnumProperty implements ModelInterface, ArrayAccess, \JsonS
         return self::$openAPIFormats;
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables;
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -176,7 +234,25 @@ class OuterObjectWithEnumProperty implements ModelInterface, ArrayAccess, \JsonS
      */
     public function __construct(array $data = null)
     {
-        $this->container['value'] = $data['value'] ?? null;
+        $this->setIfExists('value', $data ?? [], null);
+    }
+
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
     }
 
     /**
@@ -225,6 +301,11 @@ class OuterObjectWithEnumProperty implements ModelInterface, ArrayAccess, \JsonS
      */
     public function setValue($value)
     {
+
+        if (is_null($value)) {
+            throw new \InvalidArgumentException('non-nullable value cannot be null');
+        }
+
         $this->container['value'] = $value;
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Pet.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Pet.php
index 90963b75df1..ad237c72f08 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Pet.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Pet.php
@@ -81,6 +81,27 @@ class Pet implements ModelInterface, ArrayAccess, \JsonSerializable
         'status' => null
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        'id' => false,
+		'category' => false,
+		'name' => false,
+		'photo_urls' => false,
+		'tags' => false,
+		'status' => false
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -101,6 +122,48 @@ class Pet implements ModelInterface, ArrayAccess, \JsonSerializable
         return self::$openAPIFormats;
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables;
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -218,12 +281,30 @@ class Pet implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function __construct(array $data = null)
     {
-        $this->container['id'] = $data['id'] ?? null;
-        $this->container['category'] = $data['category'] ?? null;
-        $this->container['name'] = $data['name'] ?? null;
-        $this->container['photo_urls'] = $data['photo_urls'] ?? null;
-        $this->container['tags'] = $data['tags'] ?? null;
-        $this->container['status'] = $data['status'] ?? null;
+        $this->setIfExists('id', $data ?? [], null);
+        $this->setIfExists('category', $data ?? [], null);
+        $this->setIfExists('name', $data ?? [], null);
+        $this->setIfExists('photo_urls', $data ?? [], null);
+        $this->setIfExists('tags', $data ?? [], null);
+        $this->setIfExists('status', $data ?? [], null);
+    }
+
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
     }
 
     /**
@@ -284,6 +365,11 @@ class Pet implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setId($id)
     {
+
+        if (is_null($id)) {
+            throw new \InvalidArgumentException('non-nullable id cannot be null');
+        }
+
         $this->container['id'] = $id;
 
         return $this;
@@ -308,6 +394,11 @@ class Pet implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setCategory($category)
     {
+
+        if (is_null($category)) {
+            throw new \InvalidArgumentException('non-nullable category cannot be null');
+        }
+
         $this->container['category'] = $category;
 
         return $this;
@@ -332,6 +423,11 @@ class Pet implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setName($name)
     {
+
+        if (is_null($name)) {
+            throw new \InvalidArgumentException('non-nullable name cannot be null');
+        }
+
         $this->container['name'] = $name;
 
         return $this;
@@ -358,6 +454,11 @@ class Pet implements ModelInterface, ArrayAccess, \JsonSerializable
     {
 
 
+
+        if (is_null($photo_urls)) {
+            throw new \InvalidArgumentException('non-nullable photo_urls cannot be null');
+        }
+
         $this->container['photo_urls'] = $photo_urls;
 
         return $this;
@@ -382,6 +483,11 @@ class Pet implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setTags($tags)
     {
+
+        if (is_null($tags)) {
+            throw new \InvalidArgumentException('non-nullable tags cannot be null');
+        }
+
         $this->container['tags'] = $tags;
 
         return $this;
@@ -416,6 +522,11 @@ class Pet implements ModelInterface, ArrayAccess, \JsonSerializable
                 )
             );
         }
+
+        if (is_null($status)) {
+            throw new \InvalidArgumentException('non-nullable status cannot be null');
+        }
+
         $this->container['status'] = $status;
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ReadOnlyFirst.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ReadOnlyFirst.php
index eb8026b40a4..de98162465b 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ReadOnlyFirst.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/ReadOnlyFirst.php
@@ -73,6 +73,23 @@ class ReadOnlyFirst implements ModelInterface, ArrayAccess, \JsonSerializable
         'baz' => null
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        'bar' => false,
+		'baz' => false
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -93,6 +110,48 @@ class ReadOnlyFirst implements ModelInterface, ArrayAccess, \JsonSerializable
         return self::$openAPIFormats;
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables;
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -181,8 +240,26 @@ class ReadOnlyFirst implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function __construct(array $data = null)
     {
-        $this->container['bar'] = $data['bar'] ?? null;
-        $this->container['baz'] = $data['baz'] ?? null;
+        $this->setIfExists('bar', $data ?? [], null);
+        $this->setIfExists('baz', $data ?? [], null);
+    }
+
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
     }
 
     /**
@@ -228,6 +305,11 @@ class ReadOnlyFirst implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setBar($bar)
     {
+
+        if (is_null($bar)) {
+            throw new \InvalidArgumentException('non-nullable bar cannot be null');
+        }
+
         $this->container['bar'] = $bar;
 
         return $this;
@@ -252,6 +334,11 @@ class ReadOnlyFirst implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setBaz($baz)
     {
+
+        if (is_null($baz)) {
+            throw new \InvalidArgumentException('non-nullable baz cannot be null');
+        }
+
         $this->container['baz'] = $baz;
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/SpecialModelName.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/SpecialModelName.php
index d513b02eb31..9107149287e 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/SpecialModelName.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/SpecialModelName.php
@@ -71,6 +71,22 @@ class SpecialModelName implements ModelInterface, ArrayAccess, \JsonSerializable
         'special_property_name' => 'int64'
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        'special_property_name' => false
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -91,6 +107,48 @@ class SpecialModelName implements ModelInterface, ArrayAccess, \JsonSerializable
         return self::$openAPIFormats;
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables;
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -176,7 +234,25 @@ class SpecialModelName implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function __construct(array $data = null)
     {
-        $this->container['special_property_name'] = $data['special_property_name'] ?? null;
+        $this->setIfExists('special_property_name', $data ?? [], null);
+    }
+
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
     }
 
     /**
@@ -222,6 +298,11 @@ class SpecialModelName implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setSpecialPropertyName($special_property_name)
     {
+
+        if (is_null($special_property_name)) {
+            throw new \InvalidArgumentException('non-nullable special_property_name cannot be null');
+        }
+
         $this->container['special_property_name'] = $special_property_name;
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Tag.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Tag.php
index 3231469b242..b8a720fd3af 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Tag.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/Tag.php
@@ -73,6 +73,23 @@ class Tag implements ModelInterface, ArrayAccess, \JsonSerializable
         'name' => null
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        'id' => false,
+		'name' => false
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -93,6 +110,48 @@ class Tag implements ModelInterface, ArrayAccess, \JsonSerializable
         return self::$openAPIFormats;
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables;
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -181,8 +240,26 @@ class Tag implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function __construct(array $data = null)
     {
-        $this->container['id'] = $data['id'] ?? null;
-        $this->container['name'] = $data['name'] ?? null;
+        $this->setIfExists('id', $data ?? [], null);
+        $this->setIfExists('name', $data ?? [], null);
+    }
+
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
     }
 
     /**
@@ -228,6 +305,11 @@ class Tag implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setId($id)
     {
+
+        if (is_null($id)) {
+            throw new \InvalidArgumentException('non-nullable id cannot be null');
+        }
+
         $this->container['id'] = $id;
 
         return $this;
@@ -252,6 +334,11 @@ class Tag implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setName($name)
     {
+
+        if (is_null($name)) {
+            throw new \InvalidArgumentException('non-nullable name cannot be null');
+        }
+
         $this->container['name'] = $name;
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/User.php b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/User.php
index 1120ca6d5fa..6bafd2583bf 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/Model/User.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/Model/User.php
@@ -85,6 +85,29 @@ class User implements ModelInterface, ArrayAccess, \JsonSerializable
         'user_status' => 'int32'
     ];
 
+    /**
+      * Array of nullable properties. Used for (de)serialization
+      *
+      * @var boolean[]
+      */
+    protected static array $openAPINullables = [
+        'id' => false,
+		'username' => false,
+		'first_name' => false,
+		'last_name' => false,
+		'email' => false,
+		'password' => false,
+		'phone' => false,
+		'user_status' => false
+    ];
+
+    /**
+      * If a nullable field gets set to null, insert it here
+      *
+      * @var boolean[]
+      */
+    protected array $openAPINullablesSetToNull = [];
+
     /**
      * Array of property to type mappings. Used for (de)serialization
      *
@@ -105,6 +128,48 @@ class User implements ModelInterface, ArrayAccess, \JsonSerializable
         return self::$openAPIFormats;
     }
 
+    /**
+     * Array of nullable properties
+     *
+     * @return array
+     */
+    protected static function openAPINullables(): array
+    {
+        return self::$openAPINullables;
+    }
+
+    /**
+     * Array of nullable field names deliberately set to null
+     *
+     * @return boolean[]
+     */
+    private function getOpenAPINullablesSetToNull(): array
+    {
+        return $this->openAPINullablesSetToNull;
+    }
+
+    /**
+     * Checks if a property is nullable
+     *
+     * @param string $property
+     * @return bool
+     */
+    public static function isNullable(string $property): bool
+    {
+        return self::openAPINullables()[$property] ?? false;
+    }
+
+    /**
+     * Checks if a nullable property is set to null.
+     *
+     * @param string $property
+     * @return bool
+     */
+    public function isNullableSetToNull(string $property): bool
+    {
+        return in_array($property, $this->getOpenAPINullablesSetToNull(), true);
+    }
+
     /**
      * Array of attributes where the key is the local name,
      * and the value is the original name
@@ -211,14 +276,32 @@ class User implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function __construct(array $data = null)
     {
-        $this->container['id'] = $data['id'] ?? null;
-        $this->container['username'] = $data['username'] ?? null;
-        $this->container['first_name'] = $data['first_name'] ?? null;
-        $this->container['last_name'] = $data['last_name'] ?? null;
-        $this->container['email'] = $data['email'] ?? null;
-        $this->container['password'] = $data['password'] ?? null;
-        $this->container['phone'] = $data['phone'] ?? null;
-        $this->container['user_status'] = $data['user_status'] ?? null;
+        $this->setIfExists('id', $data ?? [], null);
+        $this->setIfExists('username', $data ?? [], null);
+        $this->setIfExists('first_name', $data ?? [], null);
+        $this->setIfExists('last_name', $data ?? [], null);
+        $this->setIfExists('email', $data ?? [], null);
+        $this->setIfExists('password', $data ?? [], null);
+        $this->setIfExists('phone', $data ?? [], null);
+        $this->setIfExists('user_status', $data ?? [], null);
+    }
+
+    /**
+    * Sets $this->container[$variableName] to the given data or to the given default Value; if $variableName
+    * is nullable and its value is set to null in the $fields array, then mark it as "set to null" in the
+    * $this->openAPINullablesSetToNull array
+    *
+    * @param string $variableName
+    * @param array  $fields
+    * @param mixed  $defaultValue
+    */
+    private function setIfExists(string $variableName, array $fields, $defaultValue): void
+    {
+        if (self::isNullable($variableName) && array_key_exists($variableName, $fields) && is_null($fields[$variableName])) {
+            $this->openAPINullablesSetToNull[] = $variableName;
+        }
+
+        $this->container[$variableName] = $fields[$variableName] ?? $defaultValue;
     }
 
     /**
@@ -264,6 +347,11 @@ class User implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setId($id)
     {
+
+        if (is_null($id)) {
+            throw new \InvalidArgumentException('non-nullable id cannot be null');
+        }
+
         $this->container['id'] = $id;
 
         return $this;
@@ -288,6 +376,11 @@ class User implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setUsername($username)
     {
+
+        if (is_null($username)) {
+            throw new \InvalidArgumentException('non-nullable username cannot be null');
+        }
+
         $this->container['username'] = $username;
 
         return $this;
@@ -312,6 +405,11 @@ class User implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setFirstName($first_name)
     {
+
+        if (is_null($first_name)) {
+            throw new \InvalidArgumentException('non-nullable first_name cannot be null');
+        }
+
         $this->container['first_name'] = $first_name;
 
         return $this;
@@ -336,6 +434,11 @@ class User implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setLastName($last_name)
     {
+
+        if (is_null($last_name)) {
+            throw new \InvalidArgumentException('non-nullable last_name cannot be null');
+        }
+
         $this->container['last_name'] = $last_name;
 
         return $this;
@@ -360,6 +463,11 @@ class User implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setEmail($email)
     {
+
+        if (is_null($email)) {
+            throw new \InvalidArgumentException('non-nullable email cannot be null');
+        }
+
         $this->container['email'] = $email;
 
         return $this;
@@ -384,6 +492,11 @@ class User implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setPassword($password)
     {
+
+        if (is_null($password)) {
+            throw new \InvalidArgumentException('non-nullable password cannot be null');
+        }
+
         $this->container['password'] = $password;
 
         return $this;
@@ -408,6 +521,11 @@ class User implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setPhone($phone)
     {
+
+        if (is_null($phone)) {
+            throw new \InvalidArgumentException('non-nullable phone cannot be null');
+        }
+
         $this->container['phone'] = $phone;
 
         return $this;
@@ -432,6 +550,11 @@ class User implements ModelInterface, ArrayAccess, \JsonSerializable
      */
     public function setUserStatus($user_status)
     {
+
+        if (is_null($user_status)) {
+            throw new \InvalidArgumentException('non-nullable user_status cannot be null');
+        }
+
         $this->container['user_status'] = $user_status;
 
         return $this;
diff --git a/samples/client/petstore/php/OpenAPIClient-php/lib/ObjectSerializer.php b/samples/client/petstore/php/OpenAPIClient-php/lib/ObjectSerializer.php
index 8395487e8f5..62756950ee2 100644
--- a/samples/client/petstore/php/OpenAPIClient-php/lib/ObjectSerializer.php
+++ b/samples/client/petstore/php/OpenAPIClient-php/lib/ObjectSerializer.php
@@ -98,7 +98,7 @@ class ObjectSerializer
                             }
                         }
                     }
-                    if ($value !== null) {
+                    if (($data::isNullable($property) && $data->isNullableSetToNull($property)) || $value !== null) {
                         $values[$data::attributeMap()[$property]] = self::sanitizeForSerialization($value, $openAPIType, $formats[$property]);
                     }
                 }
@@ -469,7 +469,15 @@ class ObjectSerializer
             foreach ($instance::openAPITypes() as $property => $type) {
                 $propertySetter = $instance::setters()[$property];
 
-                if (!isset($propertySetter) || !isset($data->{$instance::attributeMap()[$property]})) {
+                if (!isset($propertySetter)) {
+                    continue;
+                }
+
+                if (!isset($data->{$instance::attributeMap()[$property]})) {
+                    if ($instance::isNullable($property)) {
+                        $instance->$propertySetter(null);
+                    }
+
                     continue;
                 }