Customize Django comments framework so that the comment does not have to be unique

Question

I'm customizing the comments model per the Django documentation.

In my specific use case, however, comments are allowed to be blank. The trouble I get into then is that the Comment model is setup with an unique_together:

unique_together = [('user', 'comment', 'flag')]

Any ideas on how I could go about overriding this?

(...or did I start off on the wrong track with using the Comments framework altogether? :)