diff --git a/composer.json b/composer.json
index 38d36de7..7d98483f 100644
--- a/composer.json
+++ b/composer.json
@@ -28,7 +28,7 @@
         "php-amqplib/php-amqplib": "^3.3",
         "php": ">=8.4",
         "sabre/dav": "4.7.1",
-        "sabre/vobject": "dev-linagora-waiting-merges-4.5#df65b241c18c4c08cca31fb4dc71b82d231dfc06 as 4.5.7",
+        "sabre/vobject": "dev-linagora-waiting-merges-5.0.0#2ada121c9c5e76cabbf16724dda640ccbe87593d",
         "mongodb/mongodb": "^2.2",
         "monolog/monolog": "^2.9",
         "firebase/php-jwt": "^7.0"
diff --git a/lib/CalDAV/NullableUri.php b/lib/CalDAV/NullableUri.php
index c79b4d38..61d3990d 100644
--- a/lib/CalDAV/NullableUri.php
+++ b/lib/CalDAV/NullableUri.php
@@ -8,7 +8,7 @@
 class NullableUri extends Uri
 {
     #[\ReturnTypeWillChange]
-    public function offsetSet($name, $value)
+    public function offsetSet($name, $value): void
     {
         if (!$this->isNullableProperty()
             && strtoupper((string)$name) === 'VALUE'
@@ -20,7 +20,7 @@ public function offsetSet($name, $value)
         parent::offsetSet($name, $value);
     }
 
-    public function setJsonValue(array $value)
+    public function setJsonValue(array $value): void
     {
         parent::setJsonValue($this->isNullableProperty() && [null] === $value ? [''] : $value);
     }
diff --git a/lib/CalDAV/Schedule/ITipPlugin.php b/lib/CalDAV/Schedule/ITipPlugin.php
index 68c8b495..658fdb14 100644
--- a/lib/CalDAV/Schedule/ITipPlugin.php
+++ b/lib/CalDAV/Schedule/ITipPlugin.php
@@ -70,7 +70,7 @@ function iTip($request)
         $message->component = 'VEVENT';
         $message->uid = $payload->uid;
         $message->method = $issetdef('method', 'REQUEST');
-        $message->sequence = $issetdef('sequence', '0');
+        $message->sequence = (int) $issetdef('sequence', 0);
         $message->message = VObject\Reader::read($payload->ical);
         // Events coming from an external system carry the video conference link in the
         // OpenPaaS property only: expose it to the recipient's clients as well.
diff --git a/lib/CalDAV/Schedule/Plugin.php b/lib/CalDAV/Schedule/Plugin.php
index 24dcfa32..0921ffb6 100644
--- a/lib/CalDAV/Schedule/Plugin.php
+++ b/lib/CalDAV/Schedule/Plugin.php
@@ -78,7 +78,7 @@ function deliver(ITip\Message $iTipMessage) {
             $iTipMessage->message->VEVENT->SEQUENCE =0;
         }
 
-        if (!is_string($iTipMessage->recipient)) {
+        if (!isset($iTipMessage->recipient)) {
             $iTipMessage->recipient = '';
         }
 
diff --git a/tests/CalDAV/ImportPluginTest.php b/tests/CalDAV/ImportPluginTest.php
index 3e90892d..a67bfb6c 100644
--- a/tests/CalDAV/ImportPluginTest.php
+++ b/tests/CalDAV/ImportPluginTest.php
@@ -91,7 +91,7 @@ private function newItipMessage($sequence) {
 
         $message->component = 'VEVENT';
         $message->uid = 'UID';
-        $message->sequence = $sequence;
+        $message->sequence = (int) $sequence;
         $message->method = 'REQUEST';
         $message->sender = 'mailto:a@a.com';
         $message->recipient = 'mailto:b@b.com';
diff --git a/tests/CalDAV/Schedule/SchedulePluginTest.php b/tests/CalDAV/Schedule/SchedulePluginTest.php
index 664be5c5..9371a891 100644
--- a/tests/CalDAV/Schedule/SchedulePluginTest.php
+++ b/tests/CalDAV/Schedule/SchedulePluginTest.php
@@ -146,9 +146,9 @@ function testShouldPreservePublicAgendaMetadataOnOutgoingMinimalMessage() {
         $this->assertStringContainsString('X-OPENPAAS-BOOKING-LINK:booking-link-id', $serializedMessage);
     }
 
-    function testDeliverShouldNotCrashWhenRecipientIsNull() {
+    function testDeliverShouldNotCrashWhenRecipientIsMissing() {
         $message = $this->newItipMessage('1');
-        $message->recipient = null;
+        unset($message->recipient);
 
         $this->plugin->deliver($message);
 
@@ -1019,7 +1019,7 @@ private function newItipMessage($sequence) {
 
         $message->component = 'VEVENT';
         $message->uid = 'UID';
-        $message->sequence = $sequence;
+        $message->sequence = $sequence === '' ? null : (int) $sequence;
         $message->method = 'REQUEST';
         $message->sender = 'mailto:a@a.com';
         $message->recipient = 'mailto:b@b.com';
@@ -1508,6 +1508,7 @@ private function initializePluginForTeamCalendarDelivery(array $teamCalendarPriv
 
     private function newReplyMessage(string $uid, string $recipient): Message {
         $message = new Message();
+        $message->component = 'VEVENT';
         $message->method = 'REPLY';
         $message->uid = $uid;
         $message->recipient = $recipient;