I have model Foo which has field bar. The bar field should be unique, but allow nulls in it, meaning I want to allow more than one record if bar field is null,
This is fixed now that https://code.djangoproject.com/ticket/4136 is resolved. In Django 1.11+ you can use models.CharField(unique=True, null=True, blank=True) without having to manually convert blank values to None.