docs: def _current_user_manager(self, session=None):
          """Return the current user, or SYSTEM user."""
          if session is None:
              session = db.session()
  
          try:
              user = g.user
          except Exception:
              return session.query(User).get(0)
  
          if sa.orm.object_session(user) is not session:
              # this can happen when called from a celery task during development
              # (with CELERY_ALWAYS_EAGER=True): the task SA session is not
              # app.db.session, and we should not attach this object to
              # the other session, because it can make weird, hard-to-debug
              # errors related to session.identity_map.
              return session.query(User).get(user.id)
          else:
              return user