          self._files = None
          self._errors = None
  
      #####
      # Methods to determine which fields to use when (de)serializing objects.
  
      def get_default_fields(self):
 
</s> remove         self.delete = False
 </s> add  </s> remove             # Propagate errors up to our parent
            raise ValidationError(self._errors)
 </s> add             obj = self.from_native(value, files)
            if not self._errors:
                self.object = obj
                into[self.source or field_name] = self
            else:
                # Propagate errors up to our parent
                raise ValidationError(self._errors) </s> remove             into[self.source or field_name] = self
 </s> add         if value in (None, ''):
            self._delete = True
            into[(self.source or field_name)] = self </s> remove             if obj and (getattr(obj, pk_field_name) == pk_val):
                self.object = obj
                self.delete = native.get('_delete')

        obj = self.from_native(native, files)
        if not self._errors:
 </s> add  </s> remove             pk_val = native.get(pk_field_name)
 </s> add 
        self._delete = False
          self._files = None
          self._errors = None
        self._delete = False
  
      #####
      # Methods to determine which fields to use when (de)serializing objects.
  
      def get_default_fields(self):
keep add keep keep keep keep keep
 Use None to delete nested object as opposed to _delete flag 
rest_framework/serializers.py