def _migrate_subcontribution_person_links(self, old_entry):
        person_link_map = {}
        person_link_data_map = defaultdict(list)
        for speaker in getattr(old_entry, 'speakers', []):
            person = self._get_person(speaker)
            if not person:
                continue
            person_link_data = self._get_person_data(speaker)
            person_link_data_map[person].append(person_link_data)
            link = person_link_map.get(person)
            if link:
                self._update_link_data(link, person_link_data_map[person])
                self.importer.print_warning(
                    cformat('%{yellow!}Duplicated speaker "{}" for sub-contribution').format(person.full_name),
                    event_id=self.event.id
                )
            else:
                link = SubContributionPersonLink(person=person, **person_link_data)
                person_link_map[person] = link
                yield link