  
  class ForeignKeySource(RESTFrameworkModel):
      name = models.CharField(max_length=100)
      target = models.ForeignKey(ForeignKeyTarget, related_name='sources',
                                 help_text='Target', verbose_name='Target')
  
  
  # Nullable ForeignKey
  class NullableForeignKeySource(RESTFrameworkModel):
      name = models.CharField(max_length=100)
 
</s> remove                                verbose_name='Optional target object')
 </s> add                                verbose_name='Optional target object',
                               on_delete=models.CASCADE) </s> remove                                   related_name='nullable_source')
 </s> add                                   related_name='nullable_source', on_delete=models.CASCADE) </s> remove     user = models.OneToOneField(AUTH_USER_MODEL, related_name='auth_token')
 </s> add     user = models.OneToOneField(AUTH_USER_MODEL, related_name='auth_token',
                                on_delete=models.CASCADE)
                               help_text='Target', verbose_name='Target',
                               on_delete=models.CASCADE)
  
  class ForeignKeySource(RESTFrameworkModel):
      name = models.CharField(max_length=100)
      target = models.ForeignKey(ForeignKeyTarget, related_name='sources',
                               help_text='Target', verbose_name='Target',
                               on_delete=models.CASCADE)
  
  
  # Nullable ForeignKey
  class NullableForeignKeySource(RESTFrameworkModel):
      name = models.CharField(max_length=100)
keep keep keep keep replace keep keep keep keep keep
 Regarding #3729

python -Werror generates warnings informing that on_delete is a required keyword in Django 2.0 
tests/models.py