  `ModelSerializer` class and an equivalent explicit `Serializer` class.
  """
  from __future__ import unicode_literals
  
  from django.utils.translation import ugettext_lazy as _
  
  from rest_framework.compat import unicode_to_repr
  from rest_framework.exceptions import ValidationError
  from rest_framework.utils.representation import smart_repr
  
 
</s> remove         return queryset.filter(**filter_kwargs)
 </s> add         return qs_filter(queryset, **filter_kwargs) </s> remove         return queryset.filter(**filter_kwargs)
 </s> add         return qs_filter(queryset, **filter_kwargs) </s> remove         if None not in checked_values and queryset.exists():
 </s> add         if None not in checked_values and qs_exists(queryset):
from django.db import DataError
  `ModelSerializer` class and an equivalent explicit `Serializer` class.
  """
  from __future__ import unicode_literals
  
from django.db import DataError
  from django.utils.translation import ugettext_lazy as _
  
  from rest_framework.compat import unicode_to_repr
  from rest_framework.exceptions import ValidationError
  from rest_framework.utils.representation import smart_repr
  
keep keep keep add keep keep keep keep keep keep
 Robust uniqueness checks. (#4217)

* Robust uniqueness checks
* Add master to test matrix (allow_failures) 
rest_framework/validators.py