  class ChoiceFieldModel(models.Model):
      choice = models.CharField(choices=SAMPLE_CHOICES, blank=True, max_length=255)
  
  
  class NullableCharFieldModel(models.Model):
      char = models.CharField(null=True, blank=True, max_length=4)
  
  
  class ChoiceFieldModelSerializer(serializers.ModelSerializer):
      class Meta:
          model = ChoiceFieldModel
  
  
 
</s> remove         class CharFieldSerializer(serializers.ModelSerializer):
            class Meta:
                model = NullableCharFieldModel
 </s> add         class CharFieldSerializer(serializers.Serializer):
            char = serializers.CharField(allow_none=True, required=False) </s> remove         self.assertIsNone(serializer.object.char)
 </s> add         self.assertIsNone(serializer.object['char']) </s> remove                 # return None explicitly because smart_text(None) == 'None'
                # see #1834 for details
 </s> add                 # Return None explicitly because smart_text(None) == 'None'. See #1834 for details
  class ChoiceFieldModel(models.Model):
      choice = models.CharField(choices=SAMPLE_CHOICES, blank=True, max_length=255)
  
  




  class ChoiceFieldModelSerializer(serializers.ModelSerializer):
      class Meta:
          model = ChoiceFieldModel
  
  
keep keep keep keep replace replace replace replace keep keep keep keep keep
 Use Serializer instead of ModelSerializer 
tests/test_fields.py