title: NSHTTPURLResponse's initWithURL method crashes if we set header "Content-Length"
body: <p>Here's some code, where we set up an <code>NSHTTPURLResponse</code> object:</p>
  
  <pre><code>NSString * data = @"response successful";
  NSUInteger length = [data length];
  NSDictionary * headersDict = [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithUnsignedInt:length], @"Content-Length", nil];
  
  NSHTTPURLResponse * response = [[NSHTTPURLResponse alloc] initWithURL:[request URL] statusCode:200 HTTPVersion:@"1.1" headerFields:headersDict];
  </code></pre>
  
  <p>The following code will crash at the last line if we put <code>headersDict</code> as parameter. </p>
  
  <blockquote>
    <p>error: testReportAppOpenToAdMobWithAppstoreId (AdTrackerTests) failed: -[__NSCFNumber length]: unrecognized selector sent to instance 0xf653f40</p>
  </blockquote>
  
  <p>I don't know why it crashes. Debugging shows that <code>headersDict</code> is good, I suspect a bug on Apple's part. </p>
  
  <p>Any ideas?</p>