code: def get(self, identifier):
          
          logging.info('Download document with id ' + str(identifier) + '.')
          try:
              record = self.instance.get(index=self.index, doc_type=self.doc_type, id=identifier)
              if '_source' in record:
                  return record['_source']
              else:
                  return record
          except NotFoundError:
              return None
docs: Fetch document by _id.
  
          Returns None if it is not found. (Will log a warning if not found as well. Should not be used
          to search an id.)