fix: fix invalid optional parameter

Signed-off-by: Robin Appelman <robin@icewind.nl>

lib/Service/ConfigService.php

@@ -214,7 +214,7 @@ class ConfigService {
 		return $this->config->getUserValue($userId ?? $this->getUserId(), 'deck', 'attachment_folder', '/Deck');
 	}
 
-	public function setAttachmentFolder(?string $userId, string $path): void {
+	public function setAttachmentFolder(string $userId, string $path): void {
 		if ($userId === null && $this->getUserId() === null) {
 			throw new NoPermissionException('Must be logged in get the attachment folder');
 		}