Admin interface for model with optional 'self' relationship

I have a model with two foreign keys to itself:

    department = models.ForeignKey(u'self', blank = True, related_name = u'member')
    reports_to = models.ForeignKey(u'self', blank = True, related_name = u'subordinate')

When I tried to save test data from the admin interface, leaving those items blank, I got a ValueError, pasted below. What do I need to be able to save test data? I'm willing to assign non-blank values to those fields for now, but there's a chicken-and-egg problem if the admin interface won't let me save any instances until I already have an instance saved.

ValueError at /admin/directory/entity/add/

 Cannot assign None: "Entity.department" does not allow null values.

Request Method:	POST
Request URL:	http://linux:8000/admin/directory/entity/add/
Exception Type:	ValueError
Exception Value:	Cannot assign None: "Entity.department" does not allow null values.
Exception Location:	/usr/lib/pymodules/python2.6/django/db/models/fields/related.py in __set__, line 269
Python Executable:	/usr/bin/python
Python Version:	2.6.5
Python Path:	['/home/jonathan/directory', '/usr/local/lib/python2.6/dist-packages/pip-0.6.3-py2.6.egg', '/home/jonathan/store/src/satchmo/satchmo/apps', '/usr/local/lib/python2.6/dist-packages/django_threaded_multihost-1.3_3-py2.6.egg', '/usr/local/lib/python2.6/dist-packages/django_signals_ahoy-0.1_1-py2.6.egg', '/usr/local/lib/python2.6/dist-packages/django_tagging-0.3.1-py2.6.egg', '/usr/lib/python2.6', '/usr/lib/python2.6/plat-linux2', '/usr/lib/python2.6/lib-tk', '/usr/lib/python2.6/lib-old', '/usr/lib/python2.6/lib-dynload', '/usr/lib/python2.6/dist-packages', '/usr/lib/python2.6/dist-packages/PIL', '/usr/lib/python2.6/dist-packages/gst-0.10', '/usr/lib/pymodules/python2.6', '/usr/lib/python2.6/dist-packages/gtk-2.0', '/usr/lib/pymodules/python2.6/gtk-2.0', '/usr/local/lib/python2.6/dist-packages']
Server time:	Mon, 28 Jun 2010 15:13:53 -050

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