diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/PhpNextgenClientCodegen.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/PhpNextgenClientCodegen.java
index 5f84bab486d8..259916c0ebae 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/PhpNextgenClientCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/PhpNextgenClientCodegen.java
@@ -188,6 +188,7 @@ public OperationsMap postProcessOperationsWithModels(OperationsMap objs, List<Mo
         for (CodegenOperation operation : operations.getOperation()) {
             Set<String> phpReturnTypeOptions = new LinkedHashSet<>();
             Set<String> docReturnTypeOptions = new LinkedHashSet<>();
+            boolean hasEmptyResponse = false;
 
             for (CodegenResponse response : operation.responses) {
                 if (response.dataType != null) {
@@ -200,6 +201,8 @@ public OperationsMap postProcessOperationsWithModels(OperationsMap objs, List<Mo
 
                     phpReturnTypeOptions.add(returnType);
                     docReturnTypeOptions.add(response.dataType);
+                } else {
+                    hasEmptyResponse = true;
                 }
             }
 
@@ -208,9 +211,16 @@ public OperationsMap postProcessOperationsWithModels(OperationsMap objs, List<Mo
                 operation.vendorExtensions.putIfAbsent("x-php-return-type", "void");
                 operation.vendorExtensions.putIfAbsent("x-php-doc-return-type", "void");
             } else {
+                String phpReturnType = String.join("|", phpReturnTypeOptions);
+                String docReturnType = String.join("|", docReturnTypeOptions);
+                if (hasEmptyResponse) {
+                    phpReturnType = "?" + phpReturnType;
+                    docReturnType = docReturnType + "|null";
+                }
+
                 operation.vendorExtensions.putIfAbsent("x-php-return-type-is-void", false);
-                operation.vendorExtensions.putIfAbsent("x-php-return-type", String.join("|", phpReturnTypeOptions));
-                operation.vendorExtensions.putIfAbsent("x-php-doc-return-type", String.join("|", docReturnTypeOptions));
+                operation.vendorExtensions.putIfAbsent("x-php-return-type", phpReturnType);
+                operation.vendorExtensions.putIfAbsent("x-php-doc-return-type", docReturnType);
             }
 
             for (CodegenParameter param : operation.allParams) {
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/FakeApi.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/FakeApi.php
index af0936bb8aed..05d08dfd0e76 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/FakeApi.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/FakeApi.php
@@ -470,12 +470,12 @@ public function fakeBigDecimalMapRequest(
      *
      * @throws ApiException on non-2xx response or if the response body is not in the expected format
      * @throws InvalidArgumentException
-     * @return \OpenAPI\Client\Model\Error
+     * @return \OpenAPI\Client\Model\Error|null
      */
     public function fakeDeletePet(
         string $pet_id,
         string $contentType = self::contentTypes['fakeDeletePet'][0]
-    ): \OpenAPI\Client\Model\Error
+    ): ?\OpenAPI\Client\Model\Error
     {
         list($response) = $this->fakeDeletePetWithHttpInfo($pet_id, $contentType);
         return $response;
@@ -3225,12 +3225,12 @@ public function fakeWith400And4xxRangeResponseEndpointRequest(
      *
      * @throws ApiException on non-2xx response or if the response body is not in the expected format
      * @throws InvalidArgumentException
-     * @return \OpenAPI\Client\Model\Pet
+     * @return \OpenAPI\Client\Model\Pet|null
      */
     public function fakeWith400And4xxRangeResponseNo4xxDatatypeEndpoint(
         \OpenAPI\Client\Model\Pet $pet,
         string $contentType = self::contentTypes['fakeWith400And4xxRangeResponseNo4xxDatatypeEndpoint'][0]
-    ): \OpenAPI\Client\Model\Pet
+    ): ?\OpenAPI\Client\Model\Pet
     {
         list($response) = $this->fakeWith400And4xxRangeResponseNo4xxDatatypeEndpointWithHttpInfo($pet, $contentType);
         return $response;
@@ -4094,12 +4094,12 @@ public function fakeWith4xxRangeResponseEndpointRequest(
      *
      * @throws ApiException on non-2xx response or if the response body is not in the expected format
      * @throws InvalidArgumentException
-     * @return \OpenAPI\Client\Model\Pet
+     * @return \OpenAPI\Client\Model\Pet|null
      */
     public function fakeWith4xxRangeResponseNo4xxDatatypeEndpoint(
         \OpenAPI\Client\Model\Pet $pet,
         string $contentType = self::contentTypes['fakeWith4xxRangeResponseNo4xxDatatypeEndpoint'][0]
-    ): \OpenAPI\Client\Model\Pet
+    ): ?\OpenAPI\Client\Model\Pet
     {
         list($response) = $this->fakeWith4xxRangeResponseNo4xxDatatypeEndpointWithHttpInfo($pet, $contentType);
         return $response;
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/PetApi.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/PetApi.php
index ffdb74b3826c..62aacbec4d04 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/PetApi.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/PetApi.php
@@ -808,12 +808,12 @@ public function deletePetRequest(
      *
      * @throws ApiException on non-2xx response or if the response body is not in the expected format
      * @throws InvalidArgumentException
-     * @return \OpenAPI\Client\Model\Pet[]
+     * @return \OpenAPI\Client\Model\Pet[]|null
      */
     public function findPetsByStatus(
         array $status,
         string $contentType = self::contentTypes['findPetsByStatus'][0]
-    ): array
+    ): ?array
     {
         list($response) = $this->findPetsByStatusWithHttpInfo($status, $contentType);
         return $response;
@@ -1093,13 +1093,13 @@ public function findPetsByStatusRequest(
      *
      * @throws ApiException on non-2xx response or if the response body is not in the expected format
      * @throws InvalidArgumentException
-     * @return \OpenAPI\Client\Model\Pet[]
+     * @return \OpenAPI\Client\Model\Pet[]|null
      * @deprecated
      */
     public function findPetsByTags(
         array $tags,
         string $contentType = self::contentTypes['findPetsByTags'][0]
-    ): array
+    ): ?array
     {
         list($response) = $this->findPetsByTagsWithHttpInfo($tags, $contentType);
         return $response;
@@ -1383,12 +1383,12 @@ public function findPetsByTagsRequest(
      *
      * @throws ApiException on non-2xx response or if the response body is not in the expected format
      * @throws InvalidArgumentException
-     * @return \OpenAPI\Client\Model\Pet
+     * @return \OpenAPI\Client\Model\Pet|null
      */
     public function getPetById(
         int $pet_id,
         string $contentType = self::contentTypes['getPetById'][0]
-    ): \OpenAPI\Client\Model\Pet
+    ): ?\OpenAPI\Client\Model\Pet
     {
         list($response) = $this->getPetByIdWithHttpInfo($pet_id, $contentType);
         return $response;
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/StoreApi.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/StoreApi.php
index 352d81d47227..a3ac3cca2771 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/StoreApi.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/StoreApi.php
@@ -636,12 +636,12 @@ public function getInventoryRequest(
      *
      * @throws ApiException on non-2xx response or if the response body is not in the expected format
      * @throws InvalidArgumentException
-     * @return \OpenAPI\Client\Model\Order
+     * @return \OpenAPI\Client\Model\Order|null
      */
     public function getOrderById(
         int $order_id,
         string $contentType = self::contentTypes['getOrderById'][0]
-    ): \OpenAPI\Client\Model\Order
+    ): ?\OpenAPI\Client\Model\Order
     {
         list($response) = $this->getOrderByIdWithHttpInfo($order_id, $contentType);
         return $response;
@@ -922,12 +922,12 @@ public function getOrderByIdRequest(
      *
      * @throws ApiException on non-2xx response or if the response body is not in the expected format
      * @throws InvalidArgumentException
-     * @return \OpenAPI\Client\Model\Order
+     * @return \OpenAPI\Client\Model\Order|null
      */
     public function placeOrder(
         \OpenAPI\Client\Model\Order $order,
         string $contentType = self::contentTypes['placeOrder'][0]
-    ): \OpenAPI\Client\Model\Order
+    ): ?\OpenAPI\Client\Model\Order
     {
         list($response) = $this->placeOrderWithHttpInfo($order, $contentType);
         return $response;
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/UserApi.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/UserApi.php
index e0d556285746..0483a7812be2 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/UserApi.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/UserApi.php
@@ -1081,12 +1081,12 @@ public function deleteUserRequest(
      *
      * @throws ApiException on non-2xx response or if the response body is not in the expected format
      * @throws InvalidArgumentException
-     * @return \OpenAPI\Client\Model\User
+     * @return \OpenAPI\Client\Model\User|null
      */
     public function getUserByName(
         string $username,
         string $contentType = self::contentTypes['getUserByName'][0]
-    ): \OpenAPI\Client\Model\User
+    ): ?\OpenAPI\Client\Model\User
     {
         list($response) = $this->getUserByNameWithHttpInfo($username, $contentType);
         return $response;
@@ -1362,13 +1362,13 @@ public function getUserByNameRequest(
      *
      * @throws ApiException on non-2xx response or if the response body is not in the expected format
      * @throws InvalidArgumentException
-     * @return string
+     * @return string|null
      */
     public function loginUser(
         string $username,
         string $password,
         string $contentType = self::contentTypes['loginUser'][0]
-    ): string
+    ): ?string
     {
         list($response) = $this->loginUserWithHttpInfo($username, $password, $contentType);
         return $response;