KeyError when creating a tagged interface with a VLAN assigned

[jeremystretch]

Environment

• Python version: 3.6.9
• NetBox version: 2.7.3

Steps to Reproduce

1. Navigate to a device and add a new interface
2. Set the mode to "Tagged" and select one or more VLANs
3. Submit the interface creation form

Expected Behavior

The interface should be created with the selected VLAN(s) assigned.

Observed Behavior

A KeyError exception is raised. The full traceback is below.

Traceback:

File "/home/jstretch/.virtualenvs/netbox/lib/python3.6/site-packages/django/core/handlers/exception.py" in inner
  34.             response = get_response(request)

File "/home/jstretch/.virtualenvs/netbox/lib/python3.6/site-packages/django/core/handlers/base.py" in _get_response
  115.                 response = self.process_exception_by_middleware(e, request)

File "/home/jstretch/.virtualenvs/netbox/lib/python3.6/site-packages/django/core/handlers/base.py" in _get_response
  113.                 response = wrapped_callback(request, *callback_args, **callback_kwargs)

File "/home/jstretch/.virtualenvs/netbox/lib/python3.6/site-packages/django/views/generic/base.py" in view
  71.             return self.dispatch(request, *args, **kwargs)

File "/home/jstretch/.virtualenvs/netbox/lib/python3.6/site-packages/django/contrib/auth/mixins.py" in dispatch
  85.         return super().dispatch(request, *args, **kwargs)

File "/home/jstretch/.virtualenvs/netbox/lib/python3.6/site-packages/django/views/generic/base.py" in dispatch
  97.         return handler(request, *args, **kwargs)

File "/home/jstretch/netbox/netbox/utilities/views.py" in post
  863.         if form.is_valid():

File "/home/jstretch/.virtualenvs/netbox/lib/python3.6/site-packages/django/forms/forms.py" in is_valid
  185.         return self.is_bound and not self.errors

File "/home/jstretch/.virtualenvs/netbox/lib/python3.6/site-packages/django/forms/forms.py" in errors
  180.             self.full_clean()

File "/home/jstretch/.virtualenvs/netbox/lib/python3.6/site-packages/django/forms/forms.py" in full_clean
  382.         self._clean_form()

File "/home/jstretch/.virtualenvs/netbox/lib/python3.6/site-packages/django/forms/forms.py" in _clean_form
  409.             cleaned_data = self.clean()

File "/home/jstretch/netbox/netbox/dcim/forms.py" in clean
  113.             valid_sites = [None, self.cleaned_data['device'].site]

Exception Type: KeyError at /dcim/devices/2649/interfaces/add/
Exception Value: 'device'