def get_manipulator_new_data(self, new_data, rel=False):
        if rel:
            return new_data.get(self.name, [self.get_default()])[0]
        val = new_data.get(self.name, self.get_default())
        if not self.empty_strings_allowed and val == '' and self.null:
            val = None
        return val
Given the full new_data dictionary (from the manipulator), returns this
dataset/ETHPy150Open AppScale/appscale/AppServer/lib/django-0.96/django/db/models/fields/__init__.py/Field.get_manipulator_new_data