code: def _migrate0to1(previous: Mapping[str, Any]) -> SettingsMap:
      
      next: SettingsMap = {}
  
      for s in settings:
          id = s.id
          old_id = s.old_id
  
          if previous.get(id) is True:
              next[id] = True
          elif previous.get(old_id) is True:
              next[id] = True
          else:
              next[id] = None
  
      return next
docs: Migrate to version 1 of the feature flags file. Replaces old IDs with new
      IDs and sets any False values to None