old_contents: 
  def xroad_subsystem_path(dataset_dict):
      field_names = ('xroad_instance', 'xroad_member_code', 'xroad_subsystem_code')
      fields = [dataset_dict.get(field) for field in field_names]
      return '.'.join(fields) if all(fields) else None
  
new_contents: 
  def xroad_subsystem_path(dataset_dict):
      field_names = ('xroad_instance', 'xroad_memberclass', 'xroad_membercode', 'xroad_subsystemcode')
      fields = [dataset_dict.get(field) for field in field_names]
      return '.'.join(fields) if all(fields) else None
  
subject: Fix selecting subsystem