Don't create unnecessary histories for anon users

        Gets or creates a default history and associates it with the current

        session.

        """

        history = self.galaxy_session.current_history

        if history and not history.deleted:

            return history

        # There must be a user to fetch a default history.

        if not self.galaxy_session.user:

            return self.new_history()

        user = self.galaxy_session.user

        if user:

            # Look for default history that (a) has default name + is not deleted and

            # (b) has no datasets. If suitable history found, use it; otherwise, create

            # new history.

            stmt = select(self.app.model.History).filter_by(

            user=self.galaxy_session.user, name=self.app.model.History.default_name, deleted=False

                user=user, name=self.app.model.History.default_name, deleted=False

            )

            unnamed_histories = self.sa_session.scalars(stmt)

            default_history = None