title: How to make jq output comma separated when key is absent
body: <p>I am trying to fetch message field from below json file in comma separated value</p>
  <pre><code>[
     {
        &quot;title&quot;:&quot;second bad commit&quot;,
        &quot;message&quot;:&quot;second bad commit&quot;
     },
     {
        &quot;title&quot;:&quot;first bad commit&quot;,
        &quot;message&quot;:&quot;first bad commit&quot;,
     }
  ]
  </code></pre>
  <p>My attempt to do that with jq: <code>jq -r '.message | join(&quot;,&quot;)'</code></p>
  <p>It keeps throwing following error:
  <code>jq: error (at &lt;stdin&gt;:0): Cannot index array with string &quot;message&quot;</code></p>
  <p>So, how can I make jq output comma separated when key is absent</p>