django/django — pull request #2048 by loic (2013-12-07 16:12:43+00:00)
Title: Trigger AttributeError in ValidationError.message_dict when error_dict is missing.

The goal of this change is twofold; firstly, matching the behavior of Django 1.6
and secondly, an AttributeError is more informative than an obscure ValueError
about mismatching sequence lengths.

Refs #20867.