Apply suggestions from code review

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: auvipy

rest_framework/serializers.py

@@ -1528,6 +1528,8 @@ def get_uniqueness_extra_kwargs(self, field_names, declared_fields, extra_kwargs
                     default = ''
                 else:
                     default = empty
+            else:
+                default = empty
 
             if unique_constraint_name in model_fields:
                 # The corresponding field is present in the serializer

tests/test_validators.py

@@ -640,10 +640,11 @@ class Meta:
         constraints = [
             # Unique constraint on one required field (age) and one blank field (tag)
             models.UniqueConstraint(
-              name='unique_constraint', 
-              fields=('age', 'tag'), 
-              condition=~models.Q(models.Q(title='') & models.Q(tag='True')))
-          ]
+                name='unique_constraint',
+                fields=('age', 'tag'),
+                condition=~models.Q(tag=''),
+            )
+        ]
 
 
 class UniqueConstraintReadOnlyFieldModel(models.Model):