diff --git a/examples/ShoppingAds/AddShoppingProductListingGroupTree.php b/examples/ShoppingAds/AddShoppingProductListingGroupTree.php
index d3206a3173..aa808ee4cf 100644
--- a/examples/ShoppingAds/AddShoppingProductListingGroupTree.php
+++ b/examples/ShoppingAds/AddShoppingProductListingGroupTree.php
@@ -341,8 +341,8 @@ private static function removeListingGroupTree(
     private static function createListingGroupSubdivision(
         int $customerId,
         int $adGroupId,
-        string $parentAdGroupCriterionResourceName = null,
-        ListingDimensionInfo $listingDimensionInfo = null
+        ?string $parentAdGroupCriterionResourceName = null,
+        ?ListingDimensionInfo $listingDimensionInfo = null
     ) {
         static $tempId = 0;
         $listingGroupInfo = new ListingGroupInfo([
diff --git a/examples/Travel/AddHotelListingGroupTree.php b/examples/Travel/AddHotelListingGroupTree.php
index 469dc4ccc5..619ab6b378 100644
--- a/examples/Travel/AddHotelListingGroupTree.php
+++ b/examples/Travel/AddHotelListingGroupTree.php
@@ -365,8 +365,8 @@ private static function addLevel2Nodes(
      */
     private static function createListingGroupInfo(
         int $listingGroupType,
-        string $parentCriterionResourceName = null,
-        ListingDimensionInfo $caseValue = null
+        ?string $parentCriterionResourceName = null,
+        ?ListingDimensionInfo $caseValue = null
     ) {
         $listingGroupInfo = new ListingGroupInfo([
             'type' => $listingGroupType
diff --git a/src/Google/Ads/GoogleAds/Lib/AbstractGoogleAdsBuilder.php b/src/Google/Ads/GoogleAds/Lib/AbstractGoogleAdsBuilder.php
index f41b4c33a8..903235ba0e 100644
--- a/src/Google/Ads/GoogleAds/Lib/AbstractGoogleAdsBuilder.php
+++ b/src/Google/Ads/GoogleAds/Lib/AbstractGoogleAdsBuilder.php
@@ -30,8 +30,8 @@ abstract class AbstractGoogleAdsBuilder implements GoogleAdsBuilder
     private $environmentalVariables;
 
     public function __construct(
-        ConfigurationLoader $configurationLoader = null,
-        EnvironmentalVariables $environmentalVariables = null
+        ?ConfigurationLoader $configurationLoader = null,
+        ?EnvironmentalVariables $environmentalVariables = null
     ) {
         $this->configurationLoader = $configurationLoader ?? new ConfigurationLoader();
         $this->environmentalVariables = $environmentalVariables ?? new EnvironmentalVariables();
@@ -47,7 +47,7 @@ public function __construct(
      * @return self this builder populated from the configuration
      * @throws InvalidArgumentException if the configuration file could not be found
      */
-    public function fromFile(string $path = null): GoogleAdsBuilder
+    public function fromFile(?string $path = null): GoogleAdsBuilder
     {
         if ($path === null) {
             $path = $this->environmentalVariables->get(
diff --git a/src/Google/Ads/GoogleAds/Lib/ConfigurationLoader.php b/src/Google/Ads/GoogleAds/Lib/ConfigurationLoader.php
index 0497df455c..d78ef4a4ab 100644
--- a/src/Google/Ads/GoogleAds/Lib/ConfigurationLoader.php
+++ b/src/Google/Ads/GoogleAds/Lib/ConfigurationLoader.php
@@ -33,7 +33,7 @@ final class ConfigurationLoader
      * @param EnvironmentalVariables $environmentalVariables
      */
     public function __construct(
-        EnvironmentalVariables $environmentalVariables = null
+        ?EnvironmentalVariables $environmentalVariables = null
     ) {
         $this->environmentalVariables = $environmentalVariables ?? new EnvironmentalVariables();
     }
diff --git a/src/Google/Ads/GoogleAds/Lib/InsecureCredentialsWrapper.php b/src/Google/Ads/GoogleAds/Lib/InsecureCredentialsWrapper.php
index 5bb54c79d0..399096e5d2 100644
--- a/src/Google/Ads/GoogleAds/Lib/InsecureCredentialsWrapper.php
+++ b/src/Google/Ads/GoogleAds/Lib/InsecureCredentialsWrapper.php
@@ -36,7 +36,7 @@ class InsecureCredentialsWrapper extends CredentialsWrapper
      */
     public function __construct(
         FetchAuthTokenInterface $credentialsFetcher,
-        callable $authHttpHandler = null
+        ?callable $authHttpHandler = null
     ) {
         parent::__construct($credentialsFetcher, $authHttpHandler);
     }
diff --git a/src/Google/Ads/GoogleAds/Lib/OAuth2TokenBuilder.php b/src/Google/Ads/GoogleAds/Lib/OAuth2TokenBuilder.php
index f788caad1a..6c6ead8f80 100644
--- a/src/Google/Ads/GoogleAds/Lib/OAuth2TokenBuilder.php
+++ b/src/Google/Ads/GoogleAds/Lib/OAuth2TokenBuilder.php
@@ -47,7 +47,7 @@ final class OAuth2TokenBuilder extends AbstractGoogleAdsBuilder
     private $adcFetcher;
 
     public function __construct(
-        ConfigurationLoader $configurationLoader = null,
+        ?ConfigurationLoader $configurationLoader = null,
         ?EnvironmentalVariables $environmentalVariables = null,
     ) {
         parent::__construct($configurationLoader, $environmentalVariables);
diff --git a/src/Google/Ads/GoogleAds/Lib/V20/GoogleAdsCallLogger.php b/src/Google/Ads/GoogleAds/Lib/V20/GoogleAdsCallLogger.php
index 6cd8b6492d..384c9a5c06 100644
--- a/src/Google/Ads/GoogleAds/Lib/V20/GoogleAdsCallLogger.php
+++ b/src/Google/Ads/GoogleAds/Lib/V20/GoogleAdsCallLogger.php
@@ -63,7 +63,7 @@ public function __construct(
         LoggerInterface $logger,
         $filterLevel,
         $endpoint,
-        LogMessageFormatter $logMessageFormatter = null,
+        ?LogMessageFormatter $logMessageFormatter = null,
         $context = []
     ) {
         $this->logger = $logger;
diff --git a/src/Google/Ads/GoogleAds/Lib/V20/GoogleAdsClientBuilder.php b/src/Google/Ads/GoogleAds/Lib/V20/GoogleAdsClientBuilder.php
index 531cb32552..d03126cb83 100644
--- a/src/Google/Ads/GoogleAds/Lib/V20/GoogleAdsClientBuilder.php
+++ b/src/Google/Ads/GoogleAds/Lib/V20/GoogleAdsClientBuilder.php
@@ -70,8 +70,8 @@ final class GoogleAdsClientBuilder extends AbstractGoogleAdsBuilder
     private $adsAssistant;
 
     public function __construct(
-        ConfigurationLoader $configurationLoader = null,
-        EnvironmentalVariables $environmentalVariables = null
+        ?ConfigurationLoader $configurationLoader = null,
+        ?EnvironmentalVariables $environmentalVariables = null
     ) {
         parent::__construct($configurationLoader, $environmentalVariables);
         $this->loggerFactory = new LoggerFactory();
diff --git a/src/Google/Ads/GoogleAds/Lib/V20/InfoRedactor.php b/src/Google/Ads/GoogleAds/Lib/V20/InfoRedactor.php
index 278fd05c92..3d57a2b34c 100644
--- a/src/Google/Ads/GoogleAds/Lib/V20/InfoRedactor.php
+++ b/src/Google/Ads/GoogleAds/Lib/V20/InfoRedactor.php
@@ -93,7 +93,7 @@ public function __construct()
      */
     public function redactHeaders(
         array $headers,
-        array $headerKeysToRedactedValues = null
+        ?array $headerKeysToRedactedValues = null
     ) {
         $headerKeysToRedactedValues =
             $headerKeysToRedactedValues ?: self::getDefaultHeaderKeysToRedactedValues();
diff --git a/src/Google/Ads/GoogleAds/Lib/V20/LogMessageFormatter.php b/src/Google/Ads/GoogleAds/Lib/V20/LogMessageFormatter.php
index 58552c69e1..7d1c4616cb 100644
--- a/src/Google/Ads/GoogleAds/Lib/V20/LogMessageFormatter.php
+++ b/src/Google/Ads/GoogleAds/Lib/V20/LogMessageFormatter.php
@@ -33,8 +33,8 @@ final class LogMessageFormatter
     private $infoRedactor;
 
     public function __construct(
-        StatusMetadataExtractor $statusMetadataExtractor = null,
-        InfoRedactor $infoRedactor = null
+        ?StatusMetadataExtractor $statusMetadataExtractor = null,
+        ?InfoRedactor $infoRedactor = null
     ) {
         $this->statusMetadataExtractor = $statusMetadataExtractor ?? new StatusMetadataExtractor();
         $this->infoRedactor = $infoRedactor ?? new InfoRedactor();
diff --git a/src/Google/Ads/GoogleAds/Lib/V20/ServerStreamingGoogleAdsExceptionMiddleware.php b/src/Google/Ads/GoogleAds/Lib/V20/ServerStreamingGoogleAdsExceptionMiddleware.php
index 34b19f643b..a1abdf4c7f 100644
--- a/src/Google/Ads/GoogleAds/Lib/V20/ServerStreamingGoogleAdsExceptionMiddleware.php
+++ b/src/Google/Ads/GoogleAds/Lib/V20/ServerStreamingGoogleAdsExceptionMiddleware.php
@@ -38,8 +38,8 @@ class ServerStreamingGoogleAdsExceptionMiddleware extends GoogleAdsMiddlewareAbs
      * @param StatusMetadataExtractor|null $statusMetadataExtractor
      */
     public function __construct(
-        callable $nextHandler = null,
-        StatusMetadataExtractor $statusMetadataExtractor = null
+        ?callable $nextHandler = null,
+        ?StatusMetadataExtractor $statusMetadataExtractor = null
     ) {
         parent::__construct($nextHandler);
         $this->statusMetadataExtractor = $statusMetadataExtractor ?: new StatusMetadataExtractor();
diff --git a/src/Google/Ads/GoogleAds/Lib/V20/UnaryGoogleAdsExceptionMiddleware.php b/src/Google/Ads/GoogleAds/Lib/V20/UnaryGoogleAdsExceptionMiddleware.php
index caad0a4ce1..3cd7db104b 100644
--- a/src/Google/Ads/GoogleAds/Lib/V20/UnaryGoogleAdsExceptionMiddleware.php
+++ b/src/Google/Ads/GoogleAds/Lib/V20/UnaryGoogleAdsExceptionMiddleware.php
@@ -39,8 +39,8 @@ class UnaryGoogleAdsExceptionMiddleware extends GoogleAdsMiddlewareAbstract
      * @param StatusMetadataExtractor|null $statusMetadataExtractor
      */
     public function __construct(
-        callable $nextHandler = null,
-        StatusMetadataExtractor $statusMetadataExtractor = null
+        ?callable $nextHandler = null,
+        ?StatusMetadataExtractor $statusMetadataExtractor = null
     ) {
         parent::__construct($nextHandler);
         $this->statusMetadataExtractor = $statusMetadataExtractor ?: new StatusMetadataExtractor();
diff --git a/src/Google/Ads/GoogleAds/Lib/V20/UnaryGoogleAdsResponseMetadataCallable.php b/src/Google/Ads/GoogleAds/Lib/V20/UnaryGoogleAdsResponseMetadataCallable.php
index 2f0eb173c1..3285102efa 100644
--- a/src/Google/Ads/GoogleAds/Lib/V20/UnaryGoogleAdsResponseMetadataCallable.php
+++ b/src/Google/Ads/GoogleAds/Lib/V20/UnaryGoogleAdsResponseMetadataCallable.php
@@ -33,7 +33,7 @@ class UnaryGoogleAdsResponseMetadataCallable extends GoogleAdsMiddlewareAbstract
 
     private $adsClient;
 
-    public function __construct(callable $nextHandler = null, $adsClient = null)
+    public function __construct(?callable $nextHandler = null, $adsClient = null)
     {
         $this->adsClient = $adsClient;
         parent::__construct($nextHandler);
diff --git a/src/Google/Ads/GoogleAds/Lib/V21/GoogleAdsCallLogger.php b/src/Google/Ads/GoogleAds/Lib/V21/GoogleAdsCallLogger.php
index 203333fe7d..f67fc46a7c 100644
--- a/src/Google/Ads/GoogleAds/Lib/V21/GoogleAdsCallLogger.php
+++ b/src/Google/Ads/GoogleAds/Lib/V21/GoogleAdsCallLogger.php
@@ -63,7 +63,7 @@ public function __construct(
         LoggerInterface $logger,
         $filterLevel,
         $endpoint,
-        LogMessageFormatter $logMessageFormatter = null,
+        ?LogMessageFormatter $logMessageFormatter = null,
         $context = []
     ) {
         $this->logger = $logger;
diff --git a/src/Google/Ads/GoogleAds/Lib/V21/GoogleAdsClientBuilder.php b/src/Google/Ads/GoogleAds/Lib/V21/GoogleAdsClientBuilder.php
index 8744f0b04a..8f022e5343 100644
--- a/src/Google/Ads/GoogleAds/Lib/V21/GoogleAdsClientBuilder.php
+++ b/src/Google/Ads/GoogleAds/Lib/V21/GoogleAdsClientBuilder.php
@@ -70,8 +70,8 @@ final class GoogleAdsClientBuilder extends AbstractGoogleAdsBuilder
     private $adsAssistant;
 
     public function __construct(
-        ConfigurationLoader $configurationLoader = null,
-        EnvironmentalVariables $environmentalVariables = null
+        ?ConfigurationLoader $configurationLoader = null,
+        ?EnvironmentalVariables $environmentalVariables = null
     ) {
         parent::__construct($configurationLoader, $environmentalVariables);
         $this->loggerFactory = new LoggerFactory();
diff --git a/src/Google/Ads/GoogleAds/Lib/V21/InfoRedactor.php b/src/Google/Ads/GoogleAds/Lib/V21/InfoRedactor.php
index 368ce26b7b..eba78d7504 100644
--- a/src/Google/Ads/GoogleAds/Lib/V21/InfoRedactor.php
+++ b/src/Google/Ads/GoogleAds/Lib/V21/InfoRedactor.php
@@ -93,7 +93,7 @@ public function __construct()
      */
     public function redactHeaders(
         array $headers,
-        array $headerKeysToRedactedValues = null
+        ?array $headerKeysToRedactedValues = null
     ) {
         $headerKeysToRedactedValues =
             $headerKeysToRedactedValues ?: self::getDefaultHeaderKeysToRedactedValues();
diff --git a/src/Google/Ads/GoogleAds/Lib/V21/LogMessageFormatter.php b/src/Google/Ads/GoogleAds/Lib/V21/LogMessageFormatter.php
index 50d2851581..f0788d0765 100644
--- a/src/Google/Ads/GoogleAds/Lib/V21/LogMessageFormatter.php
+++ b/src/Google/Ads/GoogleAds/Lib/V21/LogMessageFormatter.php
@@ -33,8 +33,8 @@ final class LogMessageFormatter
     private $infoRedactor;
 
     public function __construct(
-        StatusMetadataExtractor $statusMetadataExtractor = null,
-        InfoRedactor $infoRedactor = null
+        ?StatusMetadataExtractor $statusMetadataExtractor = null,
+        ?InfoRedactor $infoRedactor = null
     ) {
         $this->statusMetadataExtractor = $statusMetadataExtractor ?? new StatusMetadataExtractor();
         $this->infoRedactor = $infoRedactor ?? new InfoRedactor();
diff --git a/src/Google/Ads/GoogleAds/Lib/V21/ServerStreamingGoogleAdsExceptionMiddleware.php b/src/Google/Ads/GoogleAds/Lib/V21/ServerStreamingGoogleAdsExceptionMiddleware.php
index f1be10d1a9..cc56589c3e 100644
--- a/src/Google/Ads/GoogleAds/Lib/V21/ServerStreamingGoogleAdsExceptionMiddleware.php
+++ b/src/Google/Ads/GoogleAds/Lib/V21/ServerStreamingGoogleAdsExceptionMiddleware.php
@@ -38,8 +38,8 @@ class ServerStreamingGoogleAdsExceptionMiddleware extends GoogleAdsMiddlewareAbs
      * @param StatusMetadataExtractor|null $statusMetadataExtractor
      */
     public function __construct(
-        callable $nextHandler = null,
-        StatusMetadataExtractor $statusMetadataExtractor = null
+        ?callable $nextHandler = null,
+        ?StatusMetadataExtractor $statusMetadataExtractor = null
     ) {
         parent::__construct($nextHandler);
         $this->statusMetadataExtractor = $statusMetadataExtractor ?: new StatusMetadataExtractor();
diff --git a/src/Google/Ads/GoogleAds/Lib/V21/UnaryGoogleAdsExceptionMiddleware.php b/src/Google/Ads/GoogleAds/Lib/V21/UnaryGoogleAdsExceptionMiddleware.php
index 105e47efc6..a6b3fc6c1b 100644
--- a/src/Google/Ads/GoogleAds/Lib/V21/UnaryGoogleAdsExceptionMiddleware.php
+++ b/src/Google/Ads/GoogleAds/Lib/V21/UnaryGoogleAdsExceptionMiddleware.php
@@ -39,8 +39,8 @@ class UnaryGoogleAdsExceptionMiddleware extends GoogleAdsMiddlewareAbstract
      * @param StatusMetadataExtractor|null $statusMetadataExtractor
      */
     public function __construct(
-        callable $nextHandler = null,
-        StatusMetadataExtractor $statusMetadataExtractor = null
+        ?callable $nextHandler = null,
+        ?StatusMetadataExtractor $statusMetadataExtractor = null
     ) {
         parent::__construct($nextHandler);
         $this->statusMetadataExtractor = $statusMetadataExtractor ?: new StatusMetadataExtractor();
diff --git a/src/Google/Ads/GoogleAds/Lib/V21/UnaryGoogleAdsResponseMetadataCallable.php b/src/Google/Ads/GoogleAds/Lib/V21/UnaryGoogleAdsResponseMetadataCallable.php
index 9e3c3a3c9e..d9c3c3aef4 100644
--- a/src/Google/Ads/GoogleAds/Lib/V21/UnaryGoogleAdsResponseMetadataCallable.php
+++ b/src/Google/Ads/GoogleAds/Lib/V21/UnaryGoogleAdsResponseMetadataCallable.php
@@ -33,7 +33,7 @@ class UnaryGoogleAdsResponseMetadataCallable extends GoogleAdsMiddlewareAbstract
 
     private $adsClient;
 
-    public function __construct(callable $nextHandler = null, $adsClient = null)
+    public function __construct(?callable $nextHandler = null, $adsClient = null)
     {
         $this->adsClient = $adsClient;
         parent::__construct($nextHandler);
diff --git a/src/Google/Ads/GoogleAds/Lib/V22/GoogleAdsCallLogger.php b/src/Google/Ads/GoogleAds/Lib/V22/GoogleAdsCallLogger.php
index 017d49ec8c..07a4524ab7 100644
--- a/src/Google/Ads/GoogleAds/Lib/V22/GoogleAdsCallLogger.php
+++ b/src/Google/Ads/GoogleAds/Lib/V22/GoogleAdsCallLogger.php
@@ -63,7 +63,7 @@ public function __construct(
         LoggerInterface $logger,
         $filterLevel,
         $endpoint,
-        LogMessageFormatter $logMessageFormatter = null,
+        ?LogMessageFormatter $logMessageFormatter = null,
         $context = []
     ) {
         $this->logger = $logger;
diff --git a/src/Google/Ads/GoogleAds/Lib/V22/GoogleAdsClientBuilder.php b/src/Google/Ads/GoogleAds/Lib/V22/GoogleAdsClientBuilder.php
index c5aba07866..9cbece9d89 100644
--- a/src/Google/Ads/GoogleAds/Lib/V22/GoogleAdsClientBuilder.php
+++ b/src/Google/Ads/GoogleAds/Lib/V22/GoogleAdsClientBuilder.php
@@ -70,8 +70,8 @@ final class GoogleAdsClientBuilder extends AbstractGoogleAdsBuilder
     private $adsAssistant;
 
     public function __construct(
-        ConfigurationLoader $configurationLoader = null,
-        EnvironmentalVariables $environmentalVariables = null
+        ?ConfigurationLoader $configurationLoader = null,
+        ?EnvironmentalVariables $environmentalVariables = null
     ) {
         parent::__construct($configurationLoader, $environmentalVariables);
         $this->loggerFactory = new LoggerFactory();
diff --git a/src/Google/Ads/GoogleAds/Lib/V22/InfoRedactor.php b/src/Google/Ads/GoogleAds/Lib/V22/InfoRedactor.php
index 0249c69a7a..555d47d452 100644
--- a/src/Google/Ads/GoogleAds/Lib/V22/InfoRedactor.php
+++ b/src/Google/Ads/GoogleAds/Lib/V22/InfoRedactor.php
@@ -93,7 +93,7 @@ public function __construct()
      */
     public function redactHeaders(
         array $headers,
-        array $headerKeysToRedactedValues = null
+        ?array $headerKeysToRedactedValues = null
     ) {
         $headerKeysToRedactedValues =
             $headerKeysToRedactedValues ?: self::getDefaultHeaderKeysToRedactedValues();
diff --git a/src/Google/Ads/GoogleAds/Lib/V22/LogMessageFormatter.php b/src/Google/Ads/GoogleAds/Lib/V22/LogMessageFormatter.php
index 65afc67e18..3a4dffc2d4 100644
--- a/src/Google/Ads/GoogleAds/Lib/V22/LogMessageFormatter.php
+++ b/src/Google/Ads/GoogleAds/Lib/V22/LogMessageFormatter.php
@@ -33,8 +33,8 @@ final class LogMessageFormatter
     private $infoRedactor;
 
     public function __construct(
-        StatusMetadataExtractor $statusMetadataExtractor = null,
-        InfoRedactor $infoRedactor = null
+        ?StatusMetadataExtractor $statusMetadataExtractor = null,
+        ?InfoRedactor $infoRedactor = null
     ) {
         $this->statusMetadataExtractor = $statusMetadataExtractor ?? new StatusMetadataExtractor();
         $this->infoRedactor = $infoRedactor ?? new InfoRedactor();
diff --git a/src/Google/Ads/GoogleAds/Lib/V22/ServerStreamingGoogleAdsExceptionMiddleware.php b/src/Google/Ads/GoogleAds/Lib/V22/ServerStreamingGoogleAdsExceptionMiddleware.php
index 6dab59fa92..359ed66d27 100644
--- a/src/Google/Ads/GoogleAds/Lib/V22/ServerStreamingGoogleAdsExceptionMiddleware.php
+++ b/src/Google/Ads/GoogleAds/Lib/V22/ServerStreamingGoogleAdsExceptionMiddleware.php
@@ -38,8 +38,8 @@ class ServerStreamingGoogleAdsExceptionMiddleware extends GoogleAdsMiddlewareAbs
      * @param StatusMetadataExtractor|null $statusMetadataExtractor
      */
     public function __construct(
-        callable $nextHandler = null,
-        StatusMetadataExtractor $statusMetadataExtractor = null
+        ?callable $nextHandler = null,
+        ?StatusMetadataExtractor $statusMetadataExtractor = null
     ) {
         parent::__construct($nextHandler);
         $this->statusMetadataExtractor = $statusMetadataExtractor ?: new StatusMetadataExtractor();
diff --git a/src/Google/Ads/GoogleAds/Lib/V23/GoogleAdsCallLogger.php b/src/Google/Ads/GoogleAds/Lib/V23/GoogleAdsCallLogger.php
index aa5174518a..8f6e43fc11 100644
--- a/src/Google/Ads/GoogleAds/Lib/V23/GoogleAdsCallLogger.php
+++ b/src/Google/Ads/GoogleAds/Lib/V23/GoogleAdsCallLogger.php
@@ -63,7 +63,7 @@ public function __construct(
         LoggerInterface $logger,
         $filterLevel,
         $endpoint,
-        LogMessageFormatter $logMessageFormatter = null,
+        ?LogMessageFormatter $logMessageFormatter = null,
         $context = []
     ) {
         $this->logger = $logger;
diff --git a/src/Google/Ads/GoogleAds/Lib/V23/GoogleAdsClientBuilder.php b/src/Google/Ads/GoogleAds/Lib/V23/GoogleAdsClientBuilder.php
index 335739e4ea..f3bba2b5aa 100644
--- a/src/Google/Ads/GoogleAds/Lib/V23/GoogleAdsClientBuilder.php
+++ b/src/Google/Ads/GoogleAds/Lib/V23/GoogleAdsClientBuilder.php
@@ -70,8 +70,8 @@ final class GoogleAdsClientBuilder extends AbstractGoogleAdsBuilder
     private $adsAssistant;
 
     public function __construct(
-        ConfigurationLoader $configurationLoader = null,
-        EnvironmentalVariables $environmentalVariables = null
+        ?ConfigurationLoader $configurationLoader = null,
+        ?EnvironmentalVariables $environmentalVariables = null
     ) {
         parent::__construct($configurationLoader, $environmentalVariables);
         $this->loggerFactory = new LoggerFactory();
diff --git a/src/Google/Ads/GoogleAds/Lib/V23/InfoRedactor.php b/src/Google/Ads/GoogleAds/Lib/V23/InfoRedactor.php
index b4870ed6f7..3c41c29e89 100644
--- a/src/Google/Ads/GoogleAds/Lib/V23/InfoRedactor.php
+++ b/src/Google/Ads/GoogleAds/Lib/V23/InfoRedactor.php
@@ -93,7 +93,7 @@ public function __construct()
      */
     public function redactHeaders(
         array $headers,
-        array $headerKeysToRedactedValues = null
+        ?array $headerKeysToRedactedValues = null
     ) {
         $headerKeysToRedactedValues =
             $headerKeysToRedactedValues ?: self::getDefaultHeaderKeysToRedactedValues();
diff --git a/src/Google/Ads/GoogleAds/Lib/V23/LogMessageFormatter.php b/src/Google/Ads/GoogleAds/Lib/V23/LogMessageFormatter.php
index a53ae96706..3b11a33b9d 100644
--- a/src/Google/Ads/GoogleAds/Lib/V23/LogMessageFormatter.php
+++ b/src/Google/Ads/GoogleAds/Lib/V23/LogMessageFormatter.php
@@ -33,8 +33,8 @@ final class LogMessageFormatter
     private $infoRedactor;
 
     public function __construct(
-        StatusMetadataExtractor $statusMetadataExtractor = null,
-        InfoRedactor $infoRedactor = null
+        ?StatusMetadataExtractor $statusMetadataExtractor = null,
+        ?InfoRedactor $infoRedactor = null
     ) {
         $this->statusMetadataExtractor = $statusMetadataExtractor ?? new StatusMetadataExtractor();
         $this->infoRedactor = $infoRedactor ?? new InfoRedactor();
diff --git a/src/Google/Ads/GoogleAds/Lib/V23/ServerStreamingGoogleAdsExceptionMiddleware.php b/src/Google/Ads/GoogleAds/Lib/V23/ServerStreamingGoogleAdsExceptionMiddleware.php
index fd331be59a..af5a0c5399 100644
--- a/src/Google/Ads/GoogleAds/Lib/V23/ServerStreamingGoogleAdsExceptionMiddleware.php
+++ b/src/Google/Ads/GoogleAds/Lib/V23/ServerStreamingGoogleAdsExceptionMiddleware.php
@@ -38,8 +38,8 @@ class ServerStreamingGoogleAdsExceptionMiddleware extends GoogleAdsMiddlewareAbs
      * @param StatusMetadataExtractor|null $statusMetadataExtractor
      */
     public function __construct(
-        callable $nextHandler = null,
-        StatusMetadataExtractor $statusMetadataExtractor = null
+        ?callable $nextHandler = null,
+        ?StatusMetadataExtractor $statusMetadataExtractor = null
     ) {
         parent::__construct($nextHandler);
         $this->statusMetadataExtractor = $statusMetadataExtractor ?: new StatusMetadataExtractor();
diff --git a/src/Google/Ads/GoogleAds/Util/ApiVersionSupport.php b/src/Google/Ads/GoogleAds/Util/ApiVersionSupport.php
index 6b6c6cdbdd..eb2489045c 100644
--- a/src/Google/Ads/GoogleAds/Util/ApiVersionSupport.php
+++ b/src/Google/Ads/GoogleAds/Util/ApiVersionSupport.php
@@ -38,7 +38,7 @@ class ApiVersionSupport
      * @param string|null $rootPath the root path of the library, the one that contains this class
      *     file is used by default
      */
-    public function __construct(string $rootPath = null)
+    public function __construct(?string $rootPath = null)
     {
         $this->rootPath = $rootPath ?: dirname(__DIR__, 5);
     }