Python 多对多字段返回None django

当我试图在终端中打印一个字段（多对多）时，我只得到结果“无”。我错过什么了吗

view.py

def assign_skill (request, pk):
    plan = get_object_or_404(Plan, pk=pk)

    if(request.GET.get('assign_skill')):
        print("nummer1")
        print(plan.title)
        print(plan.skillonplan)
    return redirect('all-plan')

models.py

class Plan(models.Model):
    user = models.ForeignKey(User, on_delete=models.CASCADE, null=True, editable=False)
    subscriber = models.ManyToManyField(User, blank = True, related_name = 'plansubscriber')
    title = models.CharField(max_length=100, default = '', null=True, blank=True)
    description = models.TextField(max_length=10000, default = '', null=True, blank=True)
    company = models.CharField(max_length=200, null=True, editable=False)
    created_date = models.DateTimeField(default=timezone.now)
    skillonplan = models.ManyToManyField(Skill, null=True, blank = True, related_name='planneke')
    duration = models.IntegerField(default=0,
    validators=[MaxValueValidator(36), MinValueValidator(1)]
    )

    def get_skills(self):
        return '\n'.join([p.skills for p in self.skill.all()])


    def __str__(self):
        return self.title

    def get_absolute_url(self):
        return reverse_lazy('plan_detail', kwargs={'pk': self.id})

---

可以使用以下代码返回多对多字段：

print(plan.skillonplan.all())