NextCloud Backup plugin throws exception on save/setup/apply

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Describe the bug
Configuring the plugin via OPNsense WebGUI results in an exception if the relative path option uses subfolders like foo/bar

To Reproduce
Steps to reproduce the behavior:

1. Install plugin
2. Go to System → Configuration → Backups → and fill in NextCloud Backup options
3. press save
4. see error

Expected behavior

• no exception
• a user friendly failure description or successful message "backup tested successfully"

Screenshots

Relevant log files

Fatal error: Uncaught TypeError: in_array(): Argument #2 ($haystack) must be of type array, null given in /usr/local/opnsense/mvc/app/library/OPNsense/Backup/Nextcloud.php:612 Stack trace: #0 /usr/local/opnsense/mvc/app/library/OPNsense/Backup/Nextcloud.php(477): OPNsense\Backup\Nextcloud->create_directory('https://files.domain.at...', 'nextcloud-username...', 'passwor...', 'nextcloud-username...', 'OPNsense-Backup...') #1 /usr/local/www/diag_backup.php(395): OPNsense\Backup\Nextcloud->backup() #2 {main} thrown in /usr/local/opnsense/mvc/app/library/OPNsense/Backup/Nextcloud.php on line 612

Additional context
I figured out, that if the directory name of the field " Directory Name without leading slash, starting from user's root" is just a word like "OPNsense", the backup works like expected.

Environment
User-Agent Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/150.0.0.0 Safari/537.36
FreeBSD 15.1-RELEASE-p1 stable/26.7-n283674-12334a596709 SMP amd64
OPNsense 26.7.1 aba53112d
Plugins os-acme-client-4.16_1 os-git-backup-1.1_3 os-nextcloud-backup-1.2 os-nginx-1.36_3 os-ntopng-1.3 os-postfix-1.24.1 os-redis-1.1_4 os-rspamd-1.13_2
Time Tue, 21 Jul 2026 22:18:28 +0200
OpenSSL 3.5.7
Python 3.13.14
PHP 8.5.8

Start in /usr/local/opnsense/mvc/app/library/OPNsense/Backup/Nextcloud.php, especially create_directory() around line 612 and its call around line 477. Reproduce the backup setup with a relative directory such as foo/bar, then verify that saving no longer throws an exception and instead reports a successful test or user-friendly failure.