Can't create VLAN resources through API with a reference to site,vlan-group

[kr3ator]

Environment

• Python version: sameas in netbox-docker
• NetBox version: 2.8.0
• This is a clean, testing installation of netbox-docker

Steps to Reproduce

1. Disable any installed plugins by commenting out the PLUGINS setting in
   configuration.py.
2. Open Netbox Swagger API interface
3. Create new VLAN-group with site defined through the API using:

curl -X POST "http://192.168.163.130:8000/api/ipam/vlan-groups/" -H "accept: application/json" -H "Content-Type: application/json" -H "X-CSRFToken: FpmEtE3MuOSNQME9PJIbXwv7pdYm1AlcUrwR9DBHnwAtkb63cm1lg0aaH6ckpsQX" -d "{ \"name\": \"DEV-GLOBAL\", \"slug\": \"dev\", \"site\": 8}"

Site 'Development' has been predefined:

{
   "id": 8,
   "name": "Development",
   "slug": "dev",
   "status": {
     "value": "active",
     "label": "Active",
     "id": 1
    },
  ......
}

No VLAN-groups had been defined.

Expected Behavior

VLAN group configured with specified parameters. Code 201 returned with return data as in the API definition.

Observed Behavior

API throws code 500 'Error: Internal Server Error'
In the response body I can see:

<pre><strong>&lt;class &#x27;AttributeError&#x27;&gt;</strong><br />
&#x27;UniqueTogetherValidator&#x27; object has no attribute &#x27;set_context&#x27;</pre>

Additional information

When reference to site ID (8) is ommited the VLAN group is created correctly.
After that, when trying to do a PATCH call to add the site to the just created vlan-group, the same error is thrown.

The same thing happens when I'm trying to create a VLAN (with site and/or group).
However, there seems to be no issues in the DCIM module as I was able to create a LAG (ref. to device id), then PATCH interface to add it to the LAG (ref. to LAG id) and finally create an IP and assign it to the interface.

Same behaviour is observed using different tools for making API requests.

[DouglasHeriot]

I ran into this as well. It's a duplicate issue of #4496 which has now been fixed in develop branch.