System page - Server Error if Custom Validation Logic is used

[moseisleydk]

Deployment Type

Self-hosted

NetBox Version

4.0.9

Python Version

3.11

Steps to Reproduce

This is also described at #17214

If I in configuration.py add a custom validator like:

from extras.validators import CustomValidator

class UniqueSerial(CustomValidator):

    def validate(self, instance):
        from dcim.models import Device

        if instance.serial and Device.objects.exclude(pk=instance.pk).filter(serial=instance.serial).exists():
            self.fail("The Serial number already exists in NetBox", field='serial')

CUSTOM_VALIDATORS = {
    'dcim.device': (
        UniqueSerial(),
    )
}

the menu item "Sytem" at /core/system/ fails with:

Object of type UniqueSerial is not JSON serializable

Python version: 3.11.6
NetBox version: 4.0.9
Plugins:
netbox_secrets: 2.0.3
netbox_topology_views: 4.0.0

Expected Behavior

The page should be rendered correct and show system data.

Observed Behavior

If I remove

CUSTOM_VALIDATORS = { 'dcim.device': ( UniqueSerial(), ) }

from configuration.py, the page renders nicely

if seems to me that the page render tries to see UniqueSerial() as a json, and not code