title: Use of undeclared identifier for "nil"
body: <p>I have just replaced all <code>NULL</code> references to <code>nil</code> in one of my code folders. But it looks like something went clearly wrong. It now shows up "Use of undeclared identifier" error for every <code>nil</code> in code.</p>
  
  <p>I have cleaned Derived Data folder.
  Restarted xCode.
  Cleaned caches and tried rebuilding many times.
  Can someone please explain what is going wrong.</p>
  
  <p>P.S.: Using xCode 7.0 beta 4 on OSX El Capitan Beta.</p>
  
  <p>Edit 1: Maybe screenshot helps: <a href="https://i.stack.imgur.com/Xe5xl.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Xe5xl.png" alt="error screenshot"></a></p>