toastdriven/django-tastypie — pull request #347 by sgarcez (2012-01-28 22:37:01+00:00)
Title: Don't throw ApiFieldError when callable attribute's queryset is empty.

This is the simplest solution I found, it was taken from https://groups.google.com/group/django-tastypie/browse_thread/thread/e3e83c1db9b47a93

If there is a better way please advise, currently it seems that callable attributes are not usable without this fix.
Thanks.