AttributeError: 'OneToOneField' object has no attribute 'model'

from django.db import models
from django.contrib.auth.models import User

class UserProfile(models.Model):
    user = models.OneToOneField(User, unique=True)
    bio = models.TextField(null=True)
    slug = models.SlugField(default=user)

    def __unicode__(self):
        return "%s's profile" % self.user

def create_profile(sender, instance, created, **kwargs):
    if created:
        profile, created = UserProfile.objects.get_or_create(user=instance)

# Signal while saving user
from django.db.models.signals import post_save
post_save.connect(create_profile, sender=User)

from django.contrib import admin
from profiles.models import UserProfile

class UserProfileAdmin(admin.ModelAdmin):
    list_display = ["user"]

admin.site.register(UserProfile, UserProfileAdmin)