diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 6ad7713..7ad8d77 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -7,7 +7,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        php-versions: ['7.4', '8.0']
+        php-versions: ['7.4', '8.0', '8.4']
 
     steps:
       - uses: actions/checkout@v2
diff --git a/.github/workflows/lint.yml b/.github/workflows/lint.yml
index 75f0f34..2cd12eb 100644
--- a/.github/workflows/lint.yml
+++ b/.github/workflows/lint.yml
@@ -6,7 +6,7 @@ jobs:
     runs-on: ubuntu-20.04
     strategy:
       matrix:
-        php-versions: ['7.4', '8.0']
+        php-versions: ['7.4', '8.0', '8.4']
     name: php${{ matrix.php-versions }} lint
     steps:
     - name: Checkout
diff --git a/src/DAV/QueryParser.php b/src/DAV/QueryParser.php
index 440b644..915184e 100644
--- a/src/DAV/QueryParser.php
+++ b/src/DAV/QueryParser.php
@@ -76,6 +76,7 @@ class QueryParser extends Service {
 			'{DAV:}contains'      => Operator::class,
 			'{DAV:}not'           => Operator::class,
 			'{DAV:}is-collection' => Operator::class,
+			'{DAV:}is-defined'    => Operator::class,
 			'{DAV:}limit'         => Limit::class,
 		];
 	}
diff --git a/src/Query/Scope.php b/src/Query/Scope.php
index faded1c..76b41ae 100644
--- a/src/Query/Scope.php
+++ b/src/Query/Scope.php
@@ -51,7 +51,7 @@ class Scope {
 	 * @param int|string $depth
 	 * @param string|null $path
 	 */
-	public function __construct(string $href = '', $depth = 1, string $path = null) {
+	public function __construct(string $href = '', $depth = 1, ?string $path = null) {
 		$this->href = $href;
 		$this->depth = $depth;
 		$this->path = $path;
diff --git a/src/XML/QueryDiscoverResponse.php b/src/XML/QueryDiscoverResponse.php
index c50dea9..0d8b6a2 100644
--- a/src/XML/QueryDiscoverResponse.php
+++ b/src/XML/QueryDiscoverResponse.php
@@ -38,7 +38,7 @@ class QueryDiscoverResponse extends Response {
 	 * @param BasicSearchSchema|null $schema
 	 * @param null|int|string $httpStatus
 	 */
-	public function __construct($href, BasicSearchSchema $schema = null, $httpStatus = null) {
+	public function __construct($href, ?BasicSearchSchema $schema = null, $httpStatus = null) {
 		if ($httpStatus !== null) {
 			$httpStatus = (string)$httpStatus;
 		}