Cannot set virtual chassis master to null using API

[jakubkrysl]

Environment

• Python version: 3.6.8
• Nautobot version: 1.2.4

I tried to remove master of virtual chassis using REST API (punautobot), but got error. The error shows on server as Bad request in django.requests. It's possible to do it in UI, but not in API. As per @glennmatthews the fix is to add allow_null=True to nautobot.dcim.api.serializers.VirtualChassisSerializer.master
See thread on Slack: https://networktocode.slack.com/archives/C01NWPK6WHL/p1645551180089729

Steps to Reproduce

1. Create virtual chassis
2. Create device
3. Add device to virtual chassis
4. Set the device as master of the virtual chassis
5. Try to clear master of the virtual chassis using API

Expected Behavior

Chassis has no master, the device is assigned to the virtual chassis

Observed Behavior

{'master': ['This field may not be null.']}