ashb commented on a change in pull request #11016:
URL: https://github.com/apache/airflow/pull/11016#discussion_r496215711
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File path: UPDATING.md
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@@ -138,6 +138,20 @@ with third party services to the ``airflow.providers``
package.
All changes made are backward compatible, but if you use the old import paths
you will
see a deprecation warning. The old import paths can be abandoned in the future.
+#### Change to undefined variable handling in templates
+
+Prior to Airflow 2.0 Jinja Templates would permit the use of undefined
variables. They would render as an
+empty string, with no indication to the user an undefined variable was used.
With this release, any template
+rendering involving undefined variables will fail the task, as well as
displaying an error in the UI when
+rendering.
+
+The behavior can be reverted when instantiating a DAG.
+```python
+import jinja2
+
+dag = DAG('simple_dag', template_undefined=jinja2.Undefined)
Review comment:
Is it also possible on a template-by-template basis to do it as `{{
something | default "x" }}`?
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