code: def add_record(self, record):
          
          record.setdefault('_oai', {}).setdefault('sets', [])
  
          assert not self.has_record(record)
  
          record['_oai']['sets'].append(self.spec)
docs: Add a record to the OAISet.
  
          :param record: Record to be added.
          :type record: `invenio_records.api.Record` or derivative.