title: Strange CLANG_WARN_NULLABLE_TO_NONNULL_CONVERSION warning
body: <p>I have activated the new compiler warning <code>CLANG_WARN_NULLABLE_TO_NONNULL_CONVERSION</code>. I could resolve most of the warnings, but one stems from a macro, and I'm not sure how to resolve the issue.</p>
  
  <p>The macro looks like this:</p>
  
  <pre><code>#define MYAssertionFail(...) [[NSAssertionHandler currentHandler] handleFailureInFunction:[NSString stringWithCString:__PRETTY_FUNCTION__ encoding:NSUTF8StringEncoding] file:[NSString stringWithCString:__FILE__ encoding:NSUTF8StringEncoding] lineNumber:__LINE__ description:__VA_ARGS__]
  </code></pre>
  
  <p>I get the following error: </p>
  
  <blockquote>
    <p>Implicit conversion from nullable pointer 'NSString * _Nullable' to
    non-nullable pointer type 'NSString * _Nonnull'</p>
  </blockquote>
  
  <p>Any idea how to rewrite the macro?</p>
  
  <p>I already tried <code>__PRAGMA_PUSH_NO_EXTRA_ARG_WARNINGS/__PRAGMA_POP_NO_EXTRA_ARG_WARNINGS</code> but it did not help.</p>