diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index 8baff649..144597a8 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -17,7 +17,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        php-version: [8.1, 8.2, 8.3]
+        php-version: [8.1, 8.2, 8.3, 8.4]
         composer: [highest, lowest]
 
     steps:
diff --git a/build/BuildMetadataFromXml.php b/build/BuildMetadataFromXml.php
index e22f8db1..09475778 100644
--- a/build/BuildMetadataFromXml.php
+++ b/build/BuildMetadataFromXml.php
@@ -585,7 +585,7 @@ public static function setPossibleLengthsGeneralDesc(PhoneNumberDesc $generalDes
      * @param int[] $lengths
      * @param int[] $localOnlyLengths
      */
-    private static function setPossibleLengths(array $lengths, array $localOnlyLengths, PhoneNumberDesc $desc, PhoneNumberDesc $parentDesc = null): void
+    private static function setPossibleLengths(array $lengths, array $localOnlyLengths, PhoneNumberDesc $desc, ?PhoneNumberDesc $parentDesc = null): void
     {
         // We clear these fields since the metadata tends to inherit from the parent element for other
         // fields (via a mergeFrom).
diff --git a/src/PhoneNumberUtil.php b/src/PhoneNumberUtil.php
index d043ce93..d8880db0 100644
--- a/src/PhoneNumberUtil.php
+++ b/src/PhoneNumberUtil.php
@@ -397,9 +397,9 @@ protected function __construct(MetadataSourceInterface $metadataSource, array $c
      */
     public static function getInstance(
         string $baseFileLocation = self::META_DATA_FILE_PREFIX,
-        array $countryCallingCodeToRegionCodeMap = null,
-        MetadataLoaderInterface $metadataLoader = null,
-        MetadataSourceInterface $metadataSource = null
+        ?array $countryCallingCodeToRegionCodeMap = null,
+        ?MetadataLoaderInterface $metadataLoader = null,
+        ?MetadataSourceInterface $metadataSource = null
     ): PhoneNumberUtil {
         if (static::$instance === null) {
             if ($countryCallingCodeToRegionCodeMap === null) {
@@ -2969,7 +2969,7 @@ public function isValidNumberForRegion(PhoneNumber $number, string $regionCode):
      *                               and the number is not in international format (does not start
      *                               with +)
      */
-    public function parse(string $numberToParse, ?string $defaultRegion = null, PhoneNumber $phoneNumber = null, bool $keepRawInput = false): PhoneNumber
+    public function parse(string $numberToParse, ?string $defaultRegion = null, ?PhoneNumber $phoneNumber = null, bool $keepRawInput = false): PhoneNumber
     {
         if ($phoneNumber === null) {
             $phoneNumber = new PhoneNumber();