old_contents: from django.db import models
  from taggit.managers import TaggableManager
  
  class Todo(models.Model):
      url = models.CharField(max_length=200, default='')
      detail = models.CharField(max_length=500, default=' ')
      tags = TaggableManager()
  
      def __str__(self):
          return self.title
  
  
new_contents: from django.db import models
  from taggit.managers import TaggableManager
  
  class Todo(models.Model):
      url = models.CharField(max_length=200, default='')
      detail = models.CharField(max_length=500, default='')
      tags = TaggableManager()
  
      def __str__(self):
          return self.title
  
  
subject: fix default for detail property