old_contents: from django.db.models import Model
  from django.utils.translation import ugettext_lazy as _
  from audit_log.models.fields import CreatingUserField, CreatingSessionKeyField, LastUserField, LastSessionKeyField
  
  class AuthStampedModel(Model):
  	"""
  	An abstract base class model that provides auth and session information
  	fields.
  	"""
  	created_by = CreatingUserField(verbose_name = _("created by"), related_name = "created_%(app_label)s_%(class)s_set")
  	created_with_session_key = CreatingSessionKeyField(_("created with session key"))
  	modified_by =  LastUserField(verbose_name = _("modified by"), related_name = "modified_%(app_label)s_%(class)s_set")
  	modified_with_session_key = LastSessionKeyField(_("modified with session key"))
  
  	class Meta:
  		abstract = True
  
new_contents: from django.db.models import Model, SET_NULL
  from django.utils.translation import ugettext_lazy as _
  from audit_log.models.fields import CreatingUserField, CreatingSessionKeyField, LastUserField, LastSessionKeyField
  
  class AuthStampedModel(Model):
  	"""
  	An abstract base class model that provides auth and session information
  	fields.
  	"""
  	created_by = CreatingUserField(on_delete=SET_NULL, null=True, verbose_name = _("created by"), related_name = "created_%(app_label)s_%(class)s_set")
  	created_with_session_key = CreatingSessionKeyField(_("created with session key"))
  	modified_by =  LastUserField(on_delete=SET_NULL, null=True, verbose_name = _("modified by"), related_name = "modified_%(app_label)s_%(class)s_set")
  	modified_with_session_key = LastSessionKeyField(_("modified with session key"))
  
  	class Meta:
  		abstract = True
  
subject: Add mandatory `on_delete` and allow nulls