diff --git a/apps/dav/lib/HookManager.php b/apps/dav/lib/HookManager.php
index 1e808e58656c4d34e33a94b442c6a1c67b8f4aa8..57b176213e091dcb70eb00ef1ef5b8e3be15a5c8 100644
--- a/apps/dav/lib/HookManager.php
+++ b/apps/dav/lib/HookManager.php
@@ -43,7 +43,7 @@ class HookManager {
 	private $syncService;
 
 	/** @var IUser[] */
-	private $usersToDelete;
+	private $usersToDelete = [];
 
 	/** @var CalDavBackend */
 	private $calDav;
@@ -52,10 +52,10 @@ class HookManager {
 	private $cardDav;
 
 	/** @var array */
-	private $calendarsToDelete;
+	private $calendarsToDelete = [];
 
 	/** @var array */
-	private $addressBooksToDelete;
+	private $addressBooksToDelete = [];
 
 	/** @var EventDispatcher */
 	private $eventDispatcher;