old_contents: from __future__ import unicode_literals
  
  from django.db import models
  
  class CommonInfo(models.Model):
      date_created = models.DateTimeField(auto_now=False, auto_now_add=True)
      date_modified = models.DateTimeField(auto_now=True, auto_now_add=False)
  
      class Meta:
          abstract = True
          
new_contents: from __future__ import unicode_literals
  
  from django.db import models
  
  class CommonInfo(models.Model):
      date_created = models.DateTimeField(auto_now_add=True)
      date_modified = models.DateTimeField(auto_now=True)
  
      class Meta:
          abstract = True
          
subject: Remove unneccessary date parameter