id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
27917	Allow ModelAdmin.radio_fields to work with NullBooleanField	Jerome Leclanche	Musen	"How to reproduce:

- Create a model with a NullBooleanField ""foo""
- Create and register a corresponding ModelAdmin instance for the model
- Add `radio_fields = {""foo"": admin.HORIZONTAL}` to the model admin

It will be rejected with a SystemCheckError:

<class 'djstripe.admin.EventAdmin'>: (admin.E023) The value of 'radio_fields' refers to 'foo', which is not an instance of ForeignKey, and does not have a 'choices' definition.

This is very unintuitive. I'm unsure why even it *needs* a choices definition seeing as it has no problem rendering a <select> widget.

Relevant links:

- https://stackoverflow.com/questions/11990852/django-display-nullbooleanfield-as-radio-and-default-to-none
- https://groups.google.com/forum/#!topic/django-users/HFU-ub1kDMw
- https://code.djangoproject.com/ticket/23681"	Cleanup/optimization	closed	contrib.admin	1.10	Normal	fixed			Accepted	0	0	0	0	0	0