From 448e56f35ecbca43e5ef095c89f14ce0a457377b Mon Sep 17 00:00:00 2001
From: Tim van Dijen <tvdijen@gmail.com>
Date: Mon, 2 Dec 2024 00:14:22 +0100
Subject: [PATCH 1/3] Bump libraries

---
 composer.json | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/composer.json b/composer.json
index b8a0c81b..f891a767 100644
--- a/composer.json
+++ b/composer.json
@@ -43,8 +43,8 @@
         "ext-pcre": "*",
         "ext-spl": "*",
 
-        "simplesamlphp/assert": "^1.3",
-        "simplesamlphp/xml-common": "^1.18.5"
+        "simplesamlphp/assert": "^1.5",
+        "simplesamlphp/xml-common": "^1.20.0"
     },
     "require-dev": {
         "simplesamlphp/simplesamlphp-test-framework": "^1.7"

From c7072b4f684cd03d5b7d864738237e8b4c9c3730 Mon Sep 17 00:00:00 2001
From: Tim van Dijen <tvdijen@gmail.com>
Date: Mon, 2 Dec 2024 00:15:06 +0100
Subject: [PATCH 2/3] Start testing PHP 8.4

---
 .github/workflows/php.yml | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/.github/workflows/php.yml b/.github/workflows/php.yml
index b5be22d8..2584f4f9 100644
--- a/.github/workflows/php.yml
+++ b/.github/workflows/php.yml
@@ -52,7 +52,7 @@ jobs:
         uses: shivammathur/setup-php@v2
         with:
           # Should be the higest supported version, so we can use the newest tools
-          php-version: '8.3'
+          php-version: '8.4'
           tools: composer, composer-require-checker, composer-unused, phpcs
           extensions: ctype, date, dom, filter, hash, mbstring, openssl, pcre, spl, xml
           coverage: none
@@ -144,7 +144,7 @@ jobs:
       fail-fast: false
       matrix:
         operating-system: [ubuntu-latest]
-        php-versions: ['8.1', '8.2', '8.3']
+        php-versions: ['8.1', '8.2', '8.3', '8.4']
 
     steps:
       - name: Print OpenSSL version
@@ -187,15 +187,15 @@ jobs:
         run: composer install --no-progress --prefer-dist --optimize-autoloader
 
       - name: Run unit tests with coverage
-        if: ${{ matrix.php-versions == '8.3' }}
+        if: ${{ matrix.php-versions == '8.4' }}
         run: vendor/bin/phpunit
 
       - name: Run unit tests (no coverage)
-        if: ${{ matrix.php-versions != '8.3' }}
+        if: ${{ matrix.php-versions != '8.4' }}
         run: vendor/bin/phpunit --no-coverage
 
       - name: Save coverage data
-        if: ${{ matrix.php-versions == '8.3' }}
+        if: ${{ matrix.php-versions == '8.4' }}
         uses: actions/upload-artifact@v4
         with:
           name: coverage-data
@@ -209,7 +209,7 @@ jobs:
       fail-fast: true
       matrix:
         operating-system: [windows-latest]
-        php-versions: ['8.1', '8.2', '8.3']
+        php-versions: ['8.1', '8.2', '8.3', '8.4']
 
     steps:
       - name: Print OpenSSL version

From 2f478b2308b06c10542488ce9690a98baaf2fdfa Mon Sep 17 00:00:00 2001
From: Tim van Dijen <tvdijen@gmail.com>
Date: Mon, 2 Dec 2024 00:21:20 +0100
Subject: [PATCH 3/3] Explicit nullable type

---
 src/Utils/XML.php                                 | 4 ++--
 src/XML/EncryptedElementTrait.php                 | 4 ++--
 src/XML/SignedElementInterface.php                | 2 +-
 src/XML/SignedElementTrait.php                    | 2 +-
 src/XML/ds/AbstractKeyInfoType.php                | 2 +-
 src/XML/ds/CanonicalizationMethod.php             | 2 +-
 src/XML/ds/DigestMethod.php                       | 2 +-
 src/XML/ds/DsObject.php                           | 2 +-
 src/XML/ds/KeyValue.php                           | 2 +-
 src/XML/ds/Manifest.php                           | 2 +-
 src/XML/ds/RSAKeyValue.php                        | 2 +-
 src/XML/ds/Reference.php                          | 2 +-
 src/XML/ds/RetrievalMethod.php                    | 2 +-
 src/XML/ds/Signature.php                          | 2 +-
 src/XML/ds/SignatureMethod.php                    | 2 +-
 src/XML/ds/SignatureProperties.php                | 2 +-
 src/XML/ds/SignatureProperty.php                  | 2 +-
 src/XML/ds/SignatureValue.php                     | 2 +-
 src/XML/ds/SignedInfo.php                         | 2 +-
 src/XML/ds/Transform.php                          | 2 +-
 src/XML/ds/Transforms.php                         | 2 +-
 src/XML/ds/X509Data.php                           | 2 +-
 src/XML/ds/X509IssuerSerial.php                   | 2 +-
 src/XML/ds/X509SerialNumber.php                   | 2 +-
 src/XML/ds/XPath.php                              | 2 +-
 src/XML/dsig11/KeyInfoReference.php               | 2 +-
 src/XML/dsig11/X509Digest.php                     | 2 +-
 src/XML/ec/InclusiveNamespaces.php                | 2 +-
 src/XML/xenc/AbstractAgreementMethodType.php      | 2 +-
 src/XML/xenc/AbstractDHKeyValueType.php           | 2 +-
 src/XML/xenc/AbstractEncryptedType.php            | 2 +-
 src/XML/xenc/AbstractEncryptionMethod.php         | 2 +-
 src/XML/xenc/AbstractEncryptionPropertiesType.php | 2 +-
 src/XML/xenc/AbstractEncryptionPropertyType.php   | 2 +-
 src/XML/xenc/AbstractReference.php                | 2 +-
 src/XML/xenc/CipherData.php                       | 2 +-
 src/XML/xenc/CipherReference.php                  | 2 +-
 src/XML/xenc/EncryptedKey.php                     | 2 +-
 src/XML/xenc/KeySize.php                          | 2 +-
 src/XML/xenc/ReferenceList.php                    | 2 +-
 src/XML/xenc/Transforms.php                       | 2 +-
 tests/XML/CustomSignable.php                      | 2 +-
 42 files changed, 44 insertions(+), 44 deletions(-)

diff --git a/src/Utils/XML.php b/src/Utils/XML.php
index e17fe16d..f2dafca5 100644
--- a/src/Utils/XML.php
+++ b/src/Utils/XML.php
@@ -33,8 +33,8 @@ class XML
     public static function canonicalizeData(
         DOMElement $element,
         string $c14nMethod,
-        array $xpaths = null,
-        array $prefixes = null,
+        ?array $xpaths = null,
+        ?array $prefixes = null,
     ): string {
         $withComments = match ($c14nMethod) {
             C::C14N_EXCLUSIVE_WITH_COMMENTS, C::C14N_INCLUSIVE_WITH_COMMENTS => true,
diff --git a/src/XML/EncryptedElementTrait.php b/src/XML/EncryptedElementTrait.php
index 5c8c9548..48b381f8 100644
--- a/src/XML/EncryptedElementTrait.php
+++ b/src/XML/EncryptedElementTrait.php
@@ -179,7 +179,7 @@ public static function fromXML(DOMElement $xml): static
     /**
      * @inheritDoc
      */
-    public function toXML(DOMElement $parent = null): DOMElement
+    public function toXML(?DOMElement $parent = null): DOMElement
     {
         $e = $this->instantiateParentElement($parent);
         $this->encryptedData->toXML($e);
@@ -196,7 +196,7 @@ public function toXML(DOMElement $parent = null): DOMElement
      * @param \DOMElement|null $parent The element we should append to.
      * @return \DOMElement
      */
-    abstract public function instantiateParentElement(DOMElement $parent = null): DOMElement;
+    abstract public function instantiateParentElement(?DOMElement $parent = null): DOMElement;
 
 
     /**
diff --git a/src/XML/SignedElementInterface.php b/src/XML/SignedElementInterface.php
index cf2e3c9a..d48ef0c3 100644
--- a/src/XML/SignedElementInterface.php
+++ b/src/XML/SignedElementInterface.php
@@ -65,5 +65,5 @@ public function isSigned(): bool;
      * in the signature.
      * @throws \SimpleSAML\XMLSecurity\Exception\RuntimeException if the signature fails to validate.
      */
-    public function verify(SignatureAlgorithmInterface $verifier = null): SignedElementInterface;
+    public function verify(?SignatureAlgorithmInterface $verifier = null): SignedElementInterface;
 }
diff --git a/src/XML/SignedElementTrait.php b/src/XML/SignedElementTrait.php
index 10b7ccbe..8fa73658 100644
--- a/src/XML/SignedElementTrait.php
+++ b/src/XML/SignedElementTrait.php
@@ -251,7 +251,7 @@ public function isSigned(): bool
      * in the signature.
      * @throws \SimpleSAML\XMLSecurity\Exception\RuntimeException if the signature fails to verify.
      */
-    public function verify(SignatureAlgorithmInterface $verifier = null): SignedElementInterface
+    public function verify(?SignatureAlgorithmInterface $verifier = null): SignedElementInterface
     {
         if (!$this->isSigned()) {
             throw new NoSignatureFoundException();
diff --git a/src/XML/ds/AbstractKeyInfoType.php b/src/XML/ds/AbstractKeyInfoType.php
index b266045f..2de04d67 100644
--- a/src/XML/ds/AbstractKeyInfoType.php
+++ b/src/XML/ds/AbstractKeyInfoType.php
@@ -100,7 +100,7 @@ public function getInfo(): array
      * @param \DOMElement|null $parent The element we should append this KeyInfo to.
      * @return \DOMElement
      */
-    public function toXML(DOMElement $parent = null): DOMElement
+    public function toXML(?DOMElement $parent = null): DOMElement
     {
         $e = $this->instantiateParentElement($parent);
 
diff --git a/src/XML/ds/CanonicalizationMethod.php b/src/XML/ds/CanonicalizationMethod.php
index f7844a3f..ddb319f5 100644
--- a/src/XML/ds/CanonicalizationMethod.php
+++ b/src/XML/ds/CanonicalizationMethod.php
@@ -78,7 +78,7 @@ public static function fromXML(DOMElement $xml): static
      * @param \DOMElement|null $parent The element we should append this KeyName element to.
      * @return \DOMElement
      */
-    public function toXML(DOMElement $parent = null): DOMElement
+    public function toXML(?DOMElement $parent = null): DOMElement
     {
         $e = $this->instantiateParentElement($parent);
         $e->setAttribute('Algorithm', $this->getAlgorithm());
diff --git a/src/XML/ds/DigestMethod.php b/src/XML/ds/DigestMethod.php
index 9ce95f54..335d5d4e 100644
--- a/src/XML/ds/DigestMethod.php
+++ b/src/XML/ds/DigestMethod.php
@@ -84,7 +84,7 @@ public static function fromXML(DOMElement $xml): static
      * @param \DOMElement|null $parent The element we should append this DigestMethod element to.
      * @return \DOMElement
      */
-    public function toXML(DOMElement $parent = null): DOMElement
+    public function toXML(?DOMElement $parent = null): DOMElement
     {
         $e = $this->instantiateParentElement($parent);
         $e->setAttribute('Algorithm', $this->getAlgorithm());
diff --git a/src/XML/ds/DsObject.php b/src/XML/ds/DsObject.php
index 72f78f5a..00f0fae0 100644
--- a/src/XML/ds/DsObject.php
+++ b/src/XML/ds/DsObject.php
@@ -123,7 +123,7 @@ public static function fromXML(DOMElement $xml): static
      * @param \DOMElement|null $parent The element we should append this ds:Object element to.
      * @return \DOMElement
      */
-    public function toXML(DOMElement $parent = null): DOMElement
+    public function toXML(?DOMElement $parent = null): DOMElement
     {
         $e = $this->instantiateParentElement($parent);
 
diff --git a/src/XML/ds/KeyValue.php b/src/XML/ds/KeyValue.php
index b6f2d018..7677371b 100644
--- a/src/XML/ds/KeyValue.php
+++ b/src/XML/ds/KeyValue.php
@@ -100,7 +100,7 @@ public static function fromXML(DOMElement $xml): static
      * @param \DOMElement|null $parent The element we should append this KeyValue element to.
      * @return \DOMElement
      */
-    public function toXML(DOMElement $parent = null): DOMElement
+    public function toXML(?DOMElement $parent = null): DOMElement
     {
         $e = $this->instantiateParentElement($parent);
 
diff --git a/src/XML/ds/Manifest.php b/src/XML/ds/Manifest.php
index b78c53cd..9eac89ab 100644
--- a/src/XML/ds/Manifest.php
+++ b/src/XML/ds/Manifest.php
@@ -88,7 +88,7 @@ public static function fromXML(DOMElement $xml): static
      * @param \DOMElement|null $parent The element we should append this Manifest element to.
      * @return \DOMElement
      */
-    public function toXML(DOMElement $parent = null): DOMElement
+    public function toXML(?DOMElement $parent = null): DOMElement
     {
         $e = $this->instantiateParentElement($parent);
 
diff --git a/src/XML/ds/RSAKeyValue.php b/src/XML/ds/RSAKeyValue.php
index 1a23e70b..ff56e935 100644
--- a/src/XML/ds/RSAKeyValue.php
+++ b/src/XML/ds/RSAKeyValue.php
@@ -104,7 +104,7 @@ public static function fromXML(DOMElement $xml): static
      * @param \DOMElement|null $parent The element we should append this RSAKeyValue element to.
      * @return \DOMElement
      */
-    public function toXML(DOMElement $parent = null): DOMElement
+    public function toXML(?DOMElement $parent = null): DOMElement
     {
         $e = $this->instantiateParentElement($parent);
 
diff --git a/src/XML/ds/Reference.php b/src/XML/ds/Reference.php
index fc7e2e83..86baeab8 100644
--- a/src/XML/ds/Reference.php
+++ b/src/XML/ds/Reference.php
@@ -167,7 +167,7 @@ public static function fromXML(DOMElement $xml): static
      * @param \DOMElement|null $parent The element we should append this Reference element to.
      * @return \DOMElement
      */
-    public function toXML(DOMElement $parent = null): DOMElement
+    public function toXML(?DOMElement $parent = null): DOMElement
     {
         $e = $this->instantiateParentElement($parent);
         if ($this->getId() !== null) {
diff --git a/src/XML/ds/RetrievalMethod.php b/src/XML/ds/RetrievalMethod.php
index e75fcca8..e14b15c4 100644
--- a/src/XML/ds/RetrievalMethod.php
+++ b/src/XML/ds/RetrievalMethod.php
@@ -100,7 +100,7 @@ public static function fromXML(DOMElement $xml): static
      * @param \DOMElement|null $parent The element we should append this RetrievalMethod element to.
      * @return \DOMElement
      */
-    public function toXML(DOMElement $parent = null): DOMElement
+    public function toXML(?DOMElement $parent = null): DOMElement
     {
         $e = $this->instantiateParentElement($parent);
         $e->setAttribute('URI', $this->getURI());
diff --git a/src/XML/ds/Signature.php b/src/XML/ds/Signature.php
index d004a314..93658706 100644
--- a/src/XML/ds/Signature.php
+++ b/src/XML/ds/Signature.php
@@ -161,7 +161,7 @@ public static function fromXML(DOMElement $xml): static
      * @param \DOMElement|null $parent The element we should append this Signature element to.
      * @return \DOMElement
      */
-    public function toXML(DOMElement $parent = null): DOMElement
+    public function toXML(?DOMElement $parent = null): DOMElement
     {
         $e = $this->instantiateParentElement($parent);
 
diff --git a/src/XML/ds/SignatureMethod.php b/src/XML/ds/SignatureMethod.php
index 095e1ecb..df2470e3 100644
--- a/src/XML/ds/SignatureMethod.php
+++ b/src/XML/ds/SignatureMethod.php
@@ -76,7 +76,7 @@ public static function fromXML(DOMElement $xml): static
      * @param \DOMElement|null $parent The element we should append this SignatureMethod element to.
      * @return \DOMElement
      */
-    public function toXML(DOMElement $parent = null): DOMElement
+    public function toXML(?DOMElement $parent = null): DOMElement
     {
         $e = $this->instantiateParentElement($parent);
         $e->setAttribute('Algorithm', $this->getAlgorithm());
diff --git a/src/XML/ds/SignatureProperties.php b/src/XML/ds/SignatureProperties.php
index cd5ff196..cb8cbe10 100644
--- a/src/XML/ds/SignatureProperties.php
+++ b/src/XML/ds/SignatureProperties.php
@@ -89,7 +89,7 @@ public static function fromXML(DOMElement $xml): static
      * @param \DOMElement|null $parent The element we should append this SignatureProperties element to.
      * @return \DOMElement
      */
-    public function toXML(DOMElement $parent = null): DOMElement
+    public function toXML(?DOMElement $parent = null): DOMElement
     {
         $e = $this->instantiateParentElement($parent);
 
diff --git a/src/XML/ds/SignatureProperty.php b/src/XML/ds/SignatureProperty.php
index c8b312c6..858b16f4 100644
--- a/src/XML/ds/SignatureProperty.php
+++ b/src/XML/ds/SignatureProperty.php
@@ -102,7 +102,7 @@ public static function fromXML(DOMElement $xml): static
      * @param \DOMElement|null $parent The element we should append this SignatureProperty element to.
      * @return \DOMElement
      */
-    public function toXML(DOMElement $parent = null): DOMElement
+    public function toXML(?DOMElement $parent = null): DOMElement
     {
         $e = $this->instantiateParentElement($parent);
         $e->setAttribute('Target', $this->getTarget());
diff --git a/src/XML/ds/SignatureValue.php b/src/XML/ds/SignatureValue.php
index d023cf4e..d90f3c7d 100644
--- a/src/XML/ds/SignatureValue.php
+++ b/src/XML/ds/SignatureValue.php
@@ -70,7 +70,7 @@ public static function fromXML(DOMElement $xml): static
      * @param \DOMElement|null $parent The element we should append this SignatureValue element to.
      * @return \DOMElement
      */
-    public function toXML(DOMElement $parent = null): DOMElement
+    public function toXML(?DOMElement $parent = null): DOMElement
     {
         $e = $this->instantiateParentElement($parent);
         $e->textContent = $this->getContent();
diff --git a/src/XML/ds/SignedInfo.php b/src/XML/ds/SignedInfo.php
index 0779cc42..4c83d61d 100644
--- a/src/XML/ds/SignedInfo.php
+++ b/src/XML/ds/SignedInfo.php
@@ -172,7 +172,7 @@ public static function fromXML(DOMElement $xml): static
      * @param \DOMElement|null $parent The element we should append this SignedInfo element to.
      * @return \DOMElement
      */
-    public function toXML(DOMElement $parent = null): DOMElement
+    public function toXML(?DOMElement $parent = null): DOMElement
     {
         $e = $this->instantiateParentElement($parent);
 
diff --git a/src/XML/ds/Transform.php b/src/XML/ds/Transform.php
index 867b4891..b18abb31 100644
--- a/src/XML/ds/Transform.php
+++ b/src/XML/ds/Transform.php
@@ -127,7 +127,7 @@ public static function fromXML(DOMElement $xml): static
      * @param \DOMElement|null $parent The element we should append this Transform element to.
      * @return \DOMElement
      */
-    public function toXML(DOMElement $parent = null): DOMElement
+    public function toXML(?DOMElement $parent = null): DOMElement
     {
         $e = $this->instantiateParentElement($parent);
 
diff --git a/src/XML/ds/Transforms.php b/src/XML/ds/Transforms.php
index db46c4fe..aef93203 100644
--- a/src/XML/ds/Transforms.php
+++ b/src/XML/ds/Transforms.php
@@ -76,7 +76,7 @@ public static function fromXML(DOMElement $xml): static
      * @param \DOMElement|null $parent The element we should append this Transforms element to.
      * @return \DOMElement
      */
-    public function toXML(DOMElement $parent = null): DOMElement
+    public function toXML(?DOMElement $parent = null): DOMElement
     {
         $e = $this->instantiateParentElement($parent);
 
diff --git a/src/XML/ds/X509Data.php b/src/XML/ds/X509Data.php
index b9c68947..d810143d 100644
--- a/src/XML/ds/X509Data.php
+++ b/src/XML/ds/X509Data.php
@@ -98,7 +98,7 @@ public static function fromXML(DOMElement $xml): static
      * @param \DOMElement|null $parent The element we should append this X509Data element to.
      * @return \DOMElement
      */
-    public function toXML(DOMElement $parent = null): DOMElement
+    public function toXML(?DOMElement $parent = null): DOMElement
     {
         $e = $this->instantiateParentElement($parent);
 
diff --git a/src/XML/ds/X509IssuerSerial.php b/src/XML/ds/X509IssuerSerial.php
index 483d1906..dc0a70da 100644
--- a/src/XML/ds/X509IssuerSerial.php
+++ b/src/XML/ds/X509IssuerSerial.php
@@ -90,7 +90,7 @@ public static function fromXML(DOMElement $xml): static
      * @param \DOMElement|null $parent The element we should append this X509IssuerSerial element to.
      * @return \DOMElement
      */
-    public function toXML(DOMElement $parent = null): DOMElement
+    public function toXML(?DOMElement $parent = null): DOMElement
     {
         $e = $this->instantiateParentElement($parent);
 
diff --git a/src/XML/ds/X509SerialNumber.php b/src/XML/ds/X509SerialNumber.php
index d7b65913..a24f19c9 100644
--- a/src/XML/ds/X509SerialNumber.php
+++ b/src/XML/ds/X509SerialNumber.php
@@ -66,7 +66,7 @@ public static function fromXML(DOMElement $xml): static
      * @param \DOMElement|null $parent The element we should append this X509SerialNumber element to.
      * @return \DOMElement
      */
-    public function toXML(DOMElement $parent = null): DOMElement
+    public function toXML(?DOMElement $parent = null): DOMElement
     {
         $e = $this->instantiateParentElement($parent);
         $e->textContent = $this->getContent();
diff --git a/src/XML/ds/XPath.php b/src/XML/ds/XPath.php
index cf84778d..087c8b17 100644
--- a/src/XML/ds/XPath.php
+++ b/src/XML/ds/XPath.php
@@ -88,7 +88,7 @@ public static function fromXML(DOMElement $xml): static
      * @param DOMElement|null $parent
      * @return DOMElement
      */
-    public function toXML(DOMElement $parent = null): DOMElement
+    public function toXML(?DOMElement $parent = null): DOMElement
     {
         $e = $this->instantiateParentElement($parent);
         $e->textContent = $this->getExpression();
diff --git a/src/XML/dsig11/KeyInfoReference.php b/src/XML/dsig11/KeyInfoReference.php
index e1bdc5f6..b9a6a78e 100644
--- a/src/XML/dsig11/KeyInfoReference.php
+++ b/src/XML/dsig11/KeyInfoReference.php
@@ -80,7 +80,7 @@ public static function fromXML(DOMElement $xml): static
      * @param \DOMElement|null $parent The element we should append this KeyInfoReference element to.
      * @return \DOMElement
      */
-    public function toXML(DOMElement $parent = null): DOMElement
+    public function toXML(?DOMElement $parent = null): DOMElement
     {
         $e = $this->instantiateParentElement($parent);
         $e->setAttribute('URI', $this->getURI());
diff --git a/src/XML/dsig11/X509Digest.php b/src/XML/dsig11/X509Digest.php
index 277dee82..0eda198a 100644
--- a/src/XML/dsig11/X509Digest.php
+++ b/src/XML/dsig11/X509Digest.php
@@ -81,7 +81,7 @@ public static function fromXML(DOMElement $xml): static
      * @param \DOMElement|null $parent The element we should append this X509Digest element to.
      * @return \DOMElement
      */
-    public function toXML(DOMElement $parent = null): DOMElement
+    public function toXML(?DOMElement $parent = null): DOMElement
     {
         $e = $this->instantiateParentElement($parent);
         $e->textContent = $this->getContent();
diff --git a/src/XML/ec/InclusiveNamespaces.php b/src/XML/ec/InclusiveNamespaces.php
index 7deff9eb..eb79c964 100644
--- a/src/XML/ec/InclusiveNamespaces.php
+++ b/src/XML/ec/InclusiveNamespaces.php
@@ -68,7 +68,7 @@ public static function fromXML(DOMElement $xml): static
      * @param \DOMElement|null $parent The element we should append this InclusiveNamespaces to.
      * @return \DOMElement
      */
-    public function toXML(DOMElement $parent = null): DOMElement
+    public function toXML(?DOMElement $parent = null): DOMElement
     {
         $e = $this->instantiateParentElement($parent);
 
diff --git a/src/XML/xenc/AbstractAgreementMethodType.php b/src/XML/xenc/AbstractAgreementMethodType.php
index 009887d0..978dbb62 100644
--- a/src/XML/xenc/AbstractAgreementMethodType.php
+++ b/src/XML/xenc/AbstractAgreementMethodType.php
@@ -140,7 +140,7 @@ public static function fromXML(DOMElement $xml): static
      * @param \DOMElement|null $parent The element we should append this AgreementMethod to.
      * @return \DOMElement
      */
-    public function toXML(DOMElement $parent = null): DOMElement
+    public function toXML(?DOMElement $parent = null): DOMElement
     {
         $e = $this->instantiateParentElement($parent);
         $e->setAttribute('Algorithm', $this->getAlgorithm());
diff --git a/src/XML/xenc/AbstractDHKeyValueType.php b/src/XML/xenc/AbstractDHKeyValueType.php
index 66b60d81..ff1afde2 100644
--- a/src/XML/xenc/AbstractDHKeyValueType.php
+++ b/src/XML/xenc/AbstractDHKeyValueType.php
@@ -172,7 +172,7 @@ public static function fromXML(DOMElement $xml): static
      * @param \DOMElement|null $parent The element we should append this DHKeyValue to.
      * @return \DOMElement
      */
-    public function toXML(DOMElement $parent = null): DOMElement
+    public function toXML(?DOMElement $parent = null): DOMElement
     {
         $e = $this->instantiateParentElement($parent);
 
diff --git a/src/XML/xenc/AbstractEncryptedType.php b/src/XML/xenc/AbstractEncryptedType.php
index 6a3e7c96..ad005c03 100644
--- a/src/XML/xenc/AbstractEncryptedType.php
+++ b/src/XML/xenc/AbstractEncryptedType.php
@@ -125,7 +125,7 @@ public function getType(): ?string
     /**
      * @inheritDoc
      */
-    public function toXML(DOMElement $parent = null): DOMElement
+    public function toXML(?DOMElement $parent = null): DOMElement
     {
         $e = $this->instantiateParentElement($parent);
 
diff --git a/src/XML/xenc/AbstractEncryptionMethod.php b/src/XML/xenc/AbstractEncryptionMethod.php
index bafc54fa..0b386162 100644
--- a/src/XML/xenc/AbstractEncryptionMethod.php
+++ b/src/XML/xenc/AbstractEncryptionMethod.php
@@ -118,7 +118,7 @@ public static function fromXML(DOMElement $xml): static
      * @param \DOMElement|null $parent The element we should append this EncryptionMethod to.
      * @return \DOMElement
      */
-    public function toXML(DOMElement $parent = null): DOMElement
+    public function toXML(?DOMElement $parent = null): DOMElement
     {
         $e = $this->instantiateParentElement($parent);
         $e->setAttribute('Algorithm', $this->getAlgorithm());
diff --git a/src/XML/xenc/AbstractEncryptionPropertiesType.php b/src/XML/xenc/AbstractEncryptionPropertiesType.php
index 63c79f3c..5b9810b8 100644
--- a/src/XML/xenc/AbstractEncryptionPropertiesType.php
+++ b/src/XML/xenc/AbstractEncryptionPropertiesType.php
@@ -75,7 +75,7 @@ public static function fromXML(DOMElement $xml): static
     /**
      * @inheritDoc
      */
-    public function toXML(DOMElement $parent = null): DOMElement
+    public function toXML(?DOMElement $parent = null): DOMElement
     {
         $e = $this->instantiateParentElement($parent);
 
diff --git a/src/XML/xenc/AbstractEncryptionPropertyType.php b/src/XML/xenc/AbstractEncryptionPropertyType.php
index 9a56bc77..a70ff237 100644
--- a/src/XML/xenc/AbstractEncryptionPropertyType.php
+++ b/src/XML/xenc/AbstractEncryptionPropertyType.php
@@ -99,7 +99,7 @@ public static function fromXML(DOMElement $xml): static
     /**
      * @inheritDoc
      */
-    public function toXML(DOMElement $parent = null): DOMElement
+    public function toXML(?DOMElement $parent = null): DOMElement
     {
         $e = $this->instantiateParentElement($parent);
 
diff --git a/src/XML/xenc/AbstractReference.php b/src/XML/xenc/AbstractReference.php
index f67f6e1d..225fdbf1 100644
--- a/src/XML/xenc/AbstractReference.php
+++ b/src/XML/xenc/AbstractReference.php
@@ -74,7 +74,7 @@ public static function fromXML(DOMElement $xml): static
     /**
      * @inheritDoc
      */
-    public function toXML(DOMElement $parent = null): DOMElement
+    public function toXML(?DOMElement $parent = null): DOMElement
     {
         $e = $this->instantiateParentElement($parent);
         $e->setAttribute('URI', $this->getUri());
diff --git a/src/XML/xenc/CipherData.php b/src/XML/xenc/CipherData.php
index 39ddc20a..3da5ac6e 100644
--- a/src/XML/xenc/CipherData.php
+++ b/src/XML/xenc/CipherData.php
@@ -100,7 +100,7 @@ public static function fromXML(DOMElement $xml): static
     /**
      * @inheritDoc
      */
-    public function toXML(DOMElement $parent = null): DOMElement
+    public function toXML(?DOMElement $parent = null): DOMElement
     {
         $e = $this->instantiateParentElement($parent);
 
diff --git a/src/XML/xenc/CipherReference.php b/src/XML/xenc/CipherReference.php
index e2a169f3..592ee0cf 100644
--- a/src/XML/xenc/CipherReference.php
+++ b/src/XML/xenc/CipherReference.php
@@ -68,7 +68,7 @@ public static function fromXML(DOMElement $xml): static
     /**
      * @inheritDoc
      */
-    public function toXML(DOMElement $parent = null): DOMElement
+    public function toXML(?DOMElement $parent = null): DOMElement
     {
         $e = $this->instantiateParentElement($parent);
         $e->setAttribute('URI', $this->getUri());
diff --git a/src/XML/xenc/EncryptedKey.php b/src/XML/xenc/EncryptedKey.php
index 76754a4e..0dcf0603 100644
--- a/src/XML/xenc/EncryptedKey.php
+++ b/src/XML/xenc/EncryptedKey.php
@@ -242,7 +242,7 @@ public static function fromXML(DOMElement $xml): static
     /**
      * @inheritDoc
      */
-    public function toXML(DOMElement $parent = null): DOMElement
+    public function toXML(?DOMElement $parent = null): DOMElement
     {
         $e = parent::toXML($parent);
 
diff --git a/src/XML/xenc/KeySize.php b/src/XML/xenc/KeySize.php
index c2faef38..c0864922 100644
--- a/src/XML/xenc/KeySize.php
+++ b/src/XML/xenc/KeySize.php
@@ -60,7 +60,7 @@ public static function fromXML(DOMElement $xml): static
      * @param \DOMElement|null $parent The element we should append this element to.
      * @return \DOMElement
      */
-    public function toXML(DOMElement $parent = null): DOMElement
+    public function toXML(?DOMElement $parent = null): DOMElement
     {
         $e = $this->instantiateParentElement($parent);
         $e->textContent = strval($this->getKeySize());
diff --git a/src/XML/xenc/ReferenceList.php b/src/XML/xenc/ReferenceList.php
index 1791b75d..537768e8 100644
--- a/src/XML/xenc/ReferenceList.php
+++ b/src/XML/xenc/ReferenceList.php
@@ -98,7 +98,7 @@ public static function fromXML(DOMElement $xml): static
     /**
      * @inheritDoc
      */
-    public function toXML(DOMElement $parent = null): DOMElement
+    public function toXML(?DOMElement $parent = null): DOMElement
     {
         $e = $this->instantiateParentElement($parent);
 
diff --git a/src/XML/xenc/Transforms.php b/src/XML/xenc/Transforms.php
index 02f20449..078f252c 100644
--- a/src/XML/xenc/Transforms.php
+++ b/src/XML/xenc/Transforms.php
@@ -77,7 +77,7 @@ public static function fromXML(DOMElement $xml): static
      * @param \DOMElement|null $parent The element we should append this Transforms element to.
      * @return \DOMElement
      */
-    public function toXML(DOMElement $parent = null): DOMElement
+    public function toXML(?DOMElement $parent = null): DOMElement
     {
         $e = $this->instantiateParentElement($parent);
 
diff --git a/tests/XML/CustomSignable.php b/tests/XML/CustomSignable.php
index 91dad755..39632086 100644
--- a/tests/XML/CustomSignable.php
+++ b/tests/XML/CustomSignable.php
@@ -182,7 +182,7 @@ public static function fromXML(DOMElement $xml): static
      * @return \DOMElement The XML element after adding the data corresponding to this CustomSignable.
      * @throws \Exception
      */
-    public function toXML(DOMElement $parent = null): DOMElement
+    public function toXML(?DOMElement $parent = null): DOMElement
     {
         if ($this->signer !== null) {
             $signedXML = $this->doSign($this->xml);