A TypeError occurs when exporting inventory items with unnamed devices

[zelfix]

Environment

• Python version: 3.6.7
• NetBox version: 2.5.7

Steps to Reproduce

1. Open the list of Inventory Items (Menu: Devices -> Inventory Items)
2. There are inventory items linked with devices without a name
3. Click the "Export" button

Expected Behavior

Download a csv file with a list of inventory items

Observed Behavior

<class 'TypeError'>
must be str, not int

Proposed solution

Change in the file 'netbox/dcim/models.py' 2426 line:

- self.device.name or '{' + self.device.pk + '}',
+ self.device.name or '{' + str(self.device.pk) + '}',