[bug] None is not of type 'object'

[luckylinux]

Describe the bug
I am seeing this in openwisp-api Docker Container Logs, when an OpenWRT is attempting to send some Monitoring Data:

Invalid data in "#/", validator says:
Apr 12 20:12:31 openwisp openwisp-api[1803]: 
Apr 12 20:12:31 openwisp openwisp-api[1803]: None is not of type 'object'

The Device managed to register but fails to ping from OpenWISP (e.g. openwisp-celery-monitoring Docker Container).

Both ping and curl work correctly in both Directions (same L2 Subnet) so the Communication should work.

Possibly related to #102

According to the Hints in that other Issue, it seems indeed to fail on netjson-monitoring, but not many Details to go by:

root@OpenWrt_OMNI_ONT_S508CL_8S_192_168_5_55:~# netjson-monitoring --dump switch.1
lua: /usr/libexec/netjson-monitoring:120: bad argument #1 to 'pairs' (table expected, got nil)
stack traceback:
	[C]: in function 'pairs'
	/usr/libexec/netjson-monitoring:120: in main chunk
	[C]: ?

Steps To Reproduce
Steps to reproduce the behavior:

1. Install the Agent on OpenWRT
2. Configure the default Template according to https://openwisp.io/docs/25.10/user/configure-device.html
3. Start the Services with /etc/init.d/openwisp-config restart and /etc/init.d/openwisp-monitoring restart
4. Check Errors on the Server: journalctl --user -xeu openwisp-api

Expected behavior
Device is Pingable and sends Monitoring Data as expected.

Screenshots

System Informatioon:

• Server OS: Fedora 43 AMD64 + Podman (Docker-like) Containers 25.10.2
• OpenWrt Version: OpenWRT 25.12.2