字段“ over_debt”没有默认值

Question

我已经在模型下方创建了该模型，并且在保存数据时出现错误字段'over_debt'没有默认值

class Debt(models.Model):
    contact = models.ForeignKey(Contacts, blank=False, verbose_name=_('Debt contact'))
    total_debt = models.DecimalField(max_digits=10, decimal_places=2, verbose_name=_('Total debt amount'))
    added_date = models.DateTimeField(null=False, blank=False)

def _get_value(self):
    days_after = self.added_date+timedelta(days=30)
    curr_date = timezone.now()
    prijt
    print(curr_date)
    if curr_date>days_after:
        return self.total_debt
    else:
        return 0    
over_debt = property(_get_value)