### Jira My PR addresses the following [AIRFLOW-2263](https://issues.apache.org/jira/browse/AIRFLOW-2263) ### Description
Remove 500-error when opening non-existent DAG in webserver UI `/admin/airflow/tree?dag_id=some_garbage` Return 404 response instead ### Tests My PR do not add new unit tests [ Full content available at: https://github.com/apache/incubator-airflow/pull/3897 ] This message was relayed via gitbox.apache.org for [email protected]
