Django-会话创建错误

Question

我从默认值为False的BooleanField中收到错误。出于某种原因，当我登录时遇到错误，指出变量（结尾）不能为null。

当我将字段更改为NullBooleanField时，我可以登录，并且当我在admin中检查实例时，该字段仍显示为空。

错误：

“结束”列中的空值违反了非空约束

models.py

class UserSessionManager(models.Manager):
    def create_new(self, user, session_key=None, ip_address=None):
        session_new = self.model()
        session_new.user = user
        session_new.session_key = session_key
        if ip_address is not None:
            city_data = get_client_city_data(ip_address)
            session_new.ip_address = ip_address
            session_new.location = Location.objects.create_new(data=city_data)
            session_new.save()
        return None

class UserSession(models.Model):
    user        = models.ForeignKey(User, blank=True, null=True)
    ip_address  = models.CharField(max_length=220, blank=True, null=True)
    session_key = models.CharField(max_length=100, blank=True, null=True)
    timestamp   = models.DateTimeField(auto_now_add=True)
    active      = models.BooleanField(default=True)
    ended       = models.BooleanField(default=False)
    location    = models.ForeignKey(Location, on_delete=models.CASCADE, related_name='location')

    objects = UserSessionManager()

    def __str__(self):
        return str(self.user.username)

    def end_session(self):
        session_key = self.session_key
        ended = self.ended
        try:
            Session.objects.get(pk=session_key).delete()
            self.active = False
            self.ended = True
            self.save()
        except:
            pass
        return self.ended

def post_save_session_receiver(sender, instance, created, *args, **kwargs):
    if created:
        qs = UserSession.objects.filter(user=instance.user, ended=False, active=False).exclude(id=instance.id)
        for i in qs:
            i.end_session()
    if not instance.active and not instance.ended:
        instance.end_session()

if FORCE_SESSION_TO_ONE:
    post_save.connect(post_save_session_receiver, sender=UserSession)

def post_save_user_changed_receiver(sender, instance, created, *args, **kwargs):
    if not created:
        if instance.is_active == False:
            qs = UserSession.objects.filter(user=instance.user, ended=False, active=False)
            for i in qs:
                i.end_session()


if FORCE_INACTIVE_USER_ENDSESSION:
    post_save.connect(post_save_user_changed_receiver, sender=User)

def user_logged_in_receiver(sender, instance, request, *args, **kwargs):
    user = instance
    ip_address = get_client_ip(request)
    session_key = request.session.session_key # Django 1.11
    UserSession.objects.create_new(
            user=user,
            ip_address=ip_address,
            session_key=session_key,
        )

user_logged_in_.connect(user_logged_in_receiver)