Merge pull request #63943 from nextcloud/backport/63929/stable35

[stable35] fix(navigation): Fix undefined array key when default app is disabled

Author: susnux

lib/private/NavigationManager.php

@@ -386,7 +386,7 @@ public function setUnreadCounter(string $id, int $unreadCounter): void {
 	#[Override]
 	public function get(string $id): ?array {
 		$this->resolveAppNavigationEntries();
-		return $this->entries[$id];
+		return $this->entries[$id] ?? null;
 	}
 
 	#[Override]