title: Add space between trailer and %s only if trailer exists
body: <p>I'm trying to create a format to show something like this:</p>
  
  <p>[abbreviated-hash] [issue-number] [subject]</p>
  
  <p>The issue number is a trailer that has the format "Issue: [issue-key]". But sometimes a commit message does not have this information.</p>
  
  <p>I wrote the following format:</p>
  
  <p><code>git log --format='%h %(trailers:key=Issue,valueonly,separator=%x2C) %s'</code></p>
  
  <p>In the cases when the issue number is not present on commit messages, this format adds two spaces between the hash abbreviation and the subject.</p>
  
  <p>How can I put this format in a way that the space between the subject and the issue number occurs only when the issue number is present?</p>
  
  <p>Here is an example of my log with that format:</p>
  
  <p><a href="https://i.stack.imgur.com/O8QLZ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/O8QLZ.png" alt="Formated log"></a></p>
  
  <p>And here is the original commit messages:</p>
  
  <p><a href="https://i.stack.imgur.com/pBVZt.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/pBVZt.png" alt="Original commit messages"></a></p>