Ansible: Perform a failed_when: on an async task based on a value from stdout

Question

I am trying to perform a failed_when: on an async task based on a value from stdout.

This is my task:

  - name: RUN SOME TASK LOCALLY
    command: <run_some_script_here>.sh
             chdir=/task_folder/
    delegate_to: localhost
    register: task_status
    async: 3600
    poll: 0

This is where I check on the task status and would like it to fail when the specified text is in stdout.

 - name: CHECK TASK PROGRESS
   async_status: jid={{ task_status.ansible_job_id }}
   register: poll_status
   until: poll_status.finished
   retries: 100
   failed_when: "'ERROR. TASK FAILED.' in poll_status.stdout"

When I run the above playbook I am faced with the following error from Ansible

TASK [CHECK TASK PROGRESS] ************************************************* 
fatal: [localhost]: FAILED! => {"failed": true, "msg": "The conditional check ''ERROR. TASK FAILED.' in poll_status.stdout' failed. The error was: error while evaluating conditional ('ERROR. TASK FAILED.' in poll_status.stdout): Unable to look up a name or access an attribute in template string ({% if 'ERROR. TASK FAILED.' in poll_status.stdout %} True {% else %} False {% endif %}).\nMake sure your variable name does not contain invalid characters like '-': argument of type 'StrictUndefined' is not iterable"}

Answer 1

You may help ansible to avoid templating crash because of undefined variable.
Change fail_when: like this:

failed_when: "poll_status.stdout is defined and 'ERROR' in poll_status.stdout"

If job is not finished by the first run of polling task, stdout is not yet populated and thus undefined, causing templating engine to crash.