title: Nil is not compatible with expected argument type 'String'
body: <p>I am currently converting my swift 2.3 code to swift 3 and I am getting the above error on the following line: </p>
  
  <pre><code>setSharedPassword(nil, account: account, completion: completion)
  </code></pre>
  
  <p>Would the appropriate solution be just to replace nil with ""? The error goes away when I do it. I am looking for an explanation. Please help. </p>