Error: __str__ returned non-string (type ModelName) in Django

Question

I am attempting to create an issue tracker similar to github's. I'm stuck on trying to implement the assigning feature, here's what I have so far

class Assign(models.Model):
    name = models.OneToOneField(User, on_delete=models.SET_NULL, null=True)
    

class Issue(models.Model):
    MARK_AS = ((True, 'Open'), (False, 'Closed'))

    title = models.CharField(max_length=100)
    content = models.TextField()
    date_posted = models.DateTimeField(default=timezone.now)
    author = models.ForeignKey(User, on_delete=models.CASCADE)
    assignee = models.ForeignKey(Assign, on_delete=models.SET_NULL, null=True)
    mark_as = models.BooleanField(choices=MARK_AS, default=True)
    

    def __str__(self):
        return self.title
    

    def get_absolute_url(self):
        return reverse('issue-detail', kwargs={'pk': self.pk})

admin page I feel like I'm close, however when I try to use

class Assign(models.Model):
    name = models.OneToOneField(User, on_delete=models.SET_NULL, null=True)
    
    def __str__(self):
        return self.name

I get the error of

__str__ returned non-string (type User)

Anyone ideas on how to fix this? Thank you.