https://github.com/apache/airflow/blob/main/airflow/cli/commands/task_command.py#L145
"""Import variables."""
        try:
            variable_dict = json.loads(request.files["file"].read())
            action_on_existing = request.form.get("action_if_exists", "overwrite").lower()
        except Exception:
            self.update_redirect()
            flash("Missing file or syntax error.", "error")
            return redirect(self.get_redirect())
        else:
            existing_keys = set()
            if action_on_existing != "overwrite":
                existing_keys = set(
                    session.scalars(select(models.Variable.key).where(models.Variable.key.in_(variable_dict)))
                )
            if action_on_existing == "fail" and existing_keys:
                failed_repr = ", ".join(repr(k) for k in sorted(existing_keys))
                flash(f"Failed. The variables with these keys: {failed_repr}  already exists.")