fix ci build, make more clear flow

rest_framework/validators.py

@@ -65,7 +65,7 @@ class UniqueValidator(object):
         try:
             exists = queryset.exists()
         except DataError:
-            return
+            exists = False
 
         if exists:
             raise ValidationError(self.message)

tests/test_validators.py

@@ -79,7 +79,7 @@ class TestUniquenessValidation(TestCase):
         data = {'ip': 'test', 'username': 'test'}
         serializer = UniquenessSerializer(data=data)
         assert not serializer.is_valid()
-        assert serializer.errors == {'ip': [u'Enter a valid IPv4 address.', u'Enter a valid IPv4 or IPv6 address.']}
+        assert serializer.errors == {'ip': ['Enter a valid IPv4 address.', 'Enter a valid IPv4 or IPv6 address.']}
 
 
 # Tests for `UniqueTogetherValidator`