title: why Xcode 7.2 crash 'Could not instantiate class named IBNSLayoutConstraint'?
body: <blockquote>
    <p>*** Terminating app due to uncaught exception
    'NSInvalidUnarchiveOperationException', reason: 'Could not instantiate
    class named IBNSLayoutConstraint'</p>
  </blockquote>
  
  <p>I just update Xcode to 7.2 then i start to check is everything alright. but I have this error and it crashes. I dig this problem, everybody said that "Make sure you don't have any constraints installed for views that aren't installed." but I don't have any uninstalled constrains. and I don't have any NSLayoutConstraint outlets.
  Thanks a lot.</p>