Can't add a new tile server
I'm trying to add a new tile server, but I'm getting an error "Failed to add tile server 'MyServer'".
**Steps to reproduce**:
1. Open GpxPod inside the nextcloud instance.
2. Click the "Settings and extra actions" button on the side panel
3. Click the "Custom tile server" tab
4. Add the following data:
```
Server name: MyServer
Server url: https://bgmtile.kade.si/{z}/{x}/{y}.png
Min zoom: 4
Max zoom: 19
```
5. Click "Add" buton
**Expected behavior**: the tile server is added to the list of custom tile servers.
**Current behavior**: an error is displayed - "Failed to add tile server 'MyServer'".
**Environment**:
```
OS: Debian 10 (Linux 4.19.0-14)
Web Server: Apache 2.4.38
PHP: v7.3.19
Nextcloud: v20.0.8
GpxPod: v4.2.8
```
When I inspect the nextcloud.log file I see the following exception: `Argument 1 passed to OCA\\GpxPod\\Controller\\UtilsController::db_quote_escape_string() must be of the type string, null given, called in /srv/http/nextcloud/apps/gpxpod/lib/Controller/UtilsController.php on line 172`
On further inspection, the `db_quote_escape_string` method in the `UtilsController.php` has a type hint set to `string`, but the `$token` variable is `null`, when the `addTileServer` function is called and subsequently `db_quote_escape_string`.
Changing the type hint to a nullable type seems to fix the issue.
issue