missing url key, plugin fails, even with ' | default('') ' about ansible-vault HOT 5 CLOSED

  - hosts: localhost
    connection: local
    gather_facts: False
    tasks:
    - name: Get a secret from Vault
~_    debug: msg="{{ lookup('file', 'user_data_file') | default('')}}"

~/src/ansible-vault/tests(master ✗) ansible-playbook test-playbook.yaml
 [WARNING]: Host file not found: /etc/ansible/hosts

 [WARNING]: provided hosts list is empty, only localhost is available


PLAY [localhost] **********************************************************************************************************************************************************

TASK [Get a secret from Vault] ********************************************************************************************************************************************
 [WARNING]: Unable to find 'user_data_file' in expected paths.

fatal: [localhost]: FAILED! => {"failed": true, "msg": "An unhandled exception occurred while running the lookup plugin 'file'. Error was a <class 'ansible.errors.AnsibleError'>, original message: could not locate file in lookup: user_data_file"}
	to retry, use: --limit @/Users/jhaals/src/ansible-vault/tests/test-playbook.retry

PLAY RECAP ****************************************************************************************************************************************************************
localhost                  : ok=0    changed=0    unreachable=0    failed=1

~/src/ansible-vault/tests(master ✗) ansible --version
ansible 2.3.2.0
  config file = /Users/jhaals/src/ansible-vault/tests/ansible.cfg
  configured module search path = Default w/o overrides
  python version = 2.7.13 (default, Jul 31 2017, 13:30:25) [GCC 4.2.1 Compatible Apple LLVM 9.0.0 (clang-900.0.31)]