docs: def convert_subject_ids(self, subject_ids):
          """
          Convert subject ids to strings if they are integers
          """
          # TODO: need to make this generalisable via a
          #       splitting+mapping function passed to the repository
          if subject_ids is not None:
              subject_ids = set(
                  ('{:03d}'.format(s)
                   if isinstance(s, int) else s) for s in subject_ids)
          return subject_ids