          if self.read_only:
              return
  
          value = data.get(field_name)
          into[(self.source or field_name)] = self.from_native(value)
  
  
  class ManyRelatedMixin(object):
      """
      Mixin to convert a related field to a many related field.
 
</s> remove             return ManyPrimaryKeyRelatedField(queryset=queryset)
        return PrimaryKeyRelatedField(queryset=queryset)
 </s> add             return ManyPrimaryKeyRelatedField(**kwargs)
        return PrimaryKeyRelatedField(**kwargs) </s> remove         response = self.detail_view(request, pk=1).render()
 </s> add         response = self.detail_view(request, pk=1) </s> remove         queryset = rel._default_manager
 </s> add  </s> remove         # # Ensure source 1 is updated, and everything else is as expected
 </s> add         # Ensure source 1 is updated, and everything else is as expected
        if value is None and not self.blank:
            raise ValidationError('Value may not be null')
        elif value is None and self.blank:
            into[(self.source or field_name)] = None
        else:
            into[(self.source or field_name)] = self.from_native(value)
          if self.read_only:
              return
  
          value = data.get(field_name)
        if value is None and not self.blank:
            raise ValidationError('Value may not be null')
        elif value is None and self.blank:
            into[(self.source or field_name)] = None
        else:
            into[(self.source or field_name)] = self.from_native(value)
  
  
  class ManyRelatedMixin(object):
      """
      Mixin to convert a related field to a many related field.
keep keep keep keep replace keep keep keep keep keep
 Support nullable FKs, with blank=True 
rest_framework/fields.py