ASN API Internal Server Error: duplicate key value violates unique constraint "uniqie_number"

[k01ek]

NetBox version
2.11.3

Describe the bug
When trying to create an ASN object via API which already exists and tenant is None, the following error occurs:

IntegrityError at /api/plugins/bgp/asn/
duplicate key value violates unique constraint "uniqie_number"
DETAIL:  Key (number)=(1) already exists.


Request Method: POST
Request URL: http://0.0.0.0:8000/api/plugins/bgp/asn/
Django Version: 3.2
Python Executable: /usr/local/bin/python
Python Version: 3.7.7
...

To Reproduce
Steps to reproduce the behavior:

1. Go to http://0.0.0.0:8000/api/docs/
2. POST New ASN with data:

{
  "number": 1,
  "status": "active",
  "description": "string"
}

3. Repeat step №2
4. See error

Expected behavior
API should return 400 Error: Bad Request with body:

{
  "__all__": [
    "Asn with this Number and Tenant already exists."
  ]
}

[k01ek]

encode/django-rest-framework#7173