title: Concatenate literal with Optional String
body: <p>Whats the proper way to implement this ? preferably in one line.</p>
  
  <pre><code>var name: String?
  ...
  let username = "@" + name
  </code></pre>
  
  <p>Note: <code>username</code> must be <code>String?</code> I don't want to unwrap <code>name</code> for concatenation.</p>
  
  <p>Edit: if <code>name</code> is <code>nil</code>, <code>username</code> should also be <code>nil</code>.</p>