code: def _evaluate(self):
          
  
          retrieved_records = SortedDict()
  
          for record_id, record in six.iteritems(self._elements):
              if record is self._field._unset:
                  # Record has not yet been retrieved, get it
                  try:
                      record = self.target_app.records.get(id=record_id)
                  except SwimlaneHTTP400Error:
                      # Record appears to be orphaned, don't include in set of elements
                      logger.debug("Received 400 response retrieving record '{}', ignoring assumed orphaned record")
                      continue
  
              retrieved_records[record_id] = record
  
          self._elements = retrieved_records
  
          return self._elements.values()
docs: Scan for orphaned records and retrieve any records that have not already been grabbed