inventory-items requires parent but not really

[Ichabond]

Issue type

[ ] Feature request
[x] Bug report
[ ] Documentation

Environment

• Python version: 3.5.2
• NetBox version: 2.2.7

Description

When doing a POST request to the /api/dcim/inventory-items endpoint with the following payload:

{'device': 1000, 'name': "EXAMPLE", 'description': "EXAMPLE", 'serial': "J219091", 'manufacturer': 1, 'part_id': "JOQ"}

It fails, with the following message:

{"name": "EXAMPLE", "description": "EXAMPLE", "part_id": "JOQ", "device": 1000, "serial": "J219091", "manufacturer": 1}, {"parent":["This field is required."]

When adding an inventory item using the UI, this field is not required (it's not even exposed), and when listing the items (using GET /api/dcim/inventory-items), parent is null.

This can be worked around by explicitly setting parent to None in the payload dictionary.