old_contents: from django.db import models
  from django.contrib.auth.models import User
  
  # Create your models here.
  # Create your models here.
  class Note(models.Model):
      # always reference the User class using setting conf
      author = models.ForeignKey(User)
      value = models.IntegerField(max_length=255)
      def __str__(self):
          return "your note is %s" % self.value
  
new_contents: from django.db import models
  from django.conf import settings
  
  # Create your models here.
  # Create your models here.
  class Note(models.Model):
      # always reference the User class using setting conf
      author = models.ForeignKey(settings.AUTH_USER_MODEL)
      value = models.IntegerField(max_length=255)
      def __str__(self):
          return "your note is %s" % self.value
  
subject: Migrate to a custom User class.