related_link_url_kwarg doesnt work with non pk value

Seems like related_link_lookup_field is not respected in SerializerMethodResourceRelatedField:

class BookSerializer(serializers.HyperlinkedModelSerializer):

    authors = relations.SerializerMethodResourceRelatedField(
        source='get_authors',
        model=Author,
        many=True,
        read_only=True,
        related_link_view_name='books-authors-list',
        related_link_url_kwarg='ext_book_id',
        related_link_lookup_field='ext_book_id',
    )

  File "/src/django-rest-framework-json-api/rest_framework_json_api/renderers.py", line 140, in extract_relationships
    field_links = field.get_links(resource_instance)
  File "/src/django-rest-framework-json-api/rest_framework_json_api/relations.py", line 125, in get_links
    related_kwargs = {self.related_link_url_kwarg: kwargs[self.related_link_lookup_field]}
KeyError: 'ext_book_id'

Looks like https://github.com/django-json-api/django-rest-framework-json-api/blob/develop/rest_framework_json_api/renderers.py#L140 get_links is missing lookup_field

kwargs: {'ext_book_id': 256} http://localhost:8000/api/books/256/authors/