在Django中计算聚合相关模型时出错

I have the following models:

我有以下型号:

class Contest(models.Model):
    id_contest = models.AutoField(primary_key=True)
    name = models.CharField(max_length=50, blank=False)

class Registration(models.Model):
    id_registration = models.AutoField(primary_key=True)
    team = models.ForeignKey(
        settings.AUTH_USER_MODEL,
        on_delete=models.DO_NOTHING,
        related_name='registrations',
        related_query_name='registration')
    contest = models.ForeignKey(
        Contest,
        on_delete=models.DO_NOTHING,
        related_name='registrations',
        related_query_name='registration')
    created_at = models.DateTimeField(null=True)
    confirmed_at = models.DateTimeField(null=True)

class Submission(models.Model):
    id_submission = models.AutoField(primary_key=True)
    team = models.ForeignKey(
        settings.AUTH_USER_MODEL,
        on_delete=models.DO_NOTHING,
        related_name='submissions',
        related_query_name='submission')
    contest = models.ForeignKey(
        Contest,
        on_delete=models.DO_NOTHING,
        related_name='submissions',
        related_query_name='submission')
    submitted_at = models.DateTimeField(null=True)
    is_valid = models.NullBooleanField()
    public_score = models.FloatField(null=True)
class