title: Pointer is missing a nullability type specifier
body: <p>In Xcode 7 GM I started to get this warning:</p>
  <blockquote>
  <p>Pointer is missing a nullability type specifier (_Nonnull, _Nullable, or _Null_unspecified)</p>
  </blockquote>
  <p>In the following function declaration (NSUserDefaults extension)</p>
  <pre><code>- (void)setObject:(nullable id)value
             forKey:(NSString *)defaultName
      objectChanged:(void(^)(NSUserDefaults *userDefaults, id value))changeHandler
      objectRamains:(void(^)(NSUserDefaults *userDefaults, id value))remainHandler;
  </code></pre>
  <p><a href="https://i.stack.imgur.com/c4TE2.png" rel="noreferrer"><img src="https://i.stack.imgur.com/c4TE2.png" alt="Screenshot" /></a></p>
  <p>Why this warning is showing and how should I fix it?</p>