title: How to catch exceptions for ansible credstash lookup plugin with key not found?
body: <p>I have the following code</p>
  
  <pre><code> app_key:   "{{ lookup('credstash', 'aws/project/'+app_name+'/'+app_env+'/app_key') | default('not-set') }}"
  </code></pre>
  
  <p>And was expecting to be able set a default value based on lookup failing with a key not found, and then generate and store a key later in my playbook.</p>
  
  <p>However, I found that the plugin raises an Exception which makes the entire playbook run fail. Obviously this is not what I was looking for (pre-storing app-keys for non production branches)</p>
  
  <p>(see credstash code: 
  You can find the credstash plugidn code here <a href="https://github.com/ansible/ansible/blob/ec701c4b82e570371af7c3999ffb587d870a5b37/lib/ansible/plugins/lookup/credstash.py" rel="nofollow noreferrer">https://github.com/ansible/ansible/blob/ec701c4b82e570371af7c3999ffb587d870a5b37/lib/ansible/plugins/lookup/credstash.py</a>) </p>
  
  <p>What are my options?</p>