title: iOS crash @ NSMutableAttributedString
body: <p>Following code crashes continuously on iOS. Please help me to find out the exact cause for this <strong>error</strong>.  </p>
  
  <pre><code>  @try {                      dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{
                  NSMutableAttributedString *attributedString =[[NSMutableAttributedString alloc]initWithData:[attrString dataUsingEncoding:NSUTF8StringEncoding] options:@{ NSDocumentTypeDocumentAttribute: NSHTMLTextDocumentType, NSCharacterEncodingDocumentAttribute:@(NSUTF8StringEncoding) } documentAttributes:nil error:nil];
                  dispatch_async(dispatch_get_main_queue(), ^{
                      //Any UI updates
                      [self.attributedLabel setAttributedText:attributedString];
                  });
              });
      }
      @catch (NSException *exception) {
          DLog(@"Trace exception : %@",exception.description);
      }
      @finally {
      }
  </code></pre>
  
  <p>And got the following message from Xcode organiser:</p>
  
  <p><a href="https://i.stack.imgur.com/7lhzD.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/7lhzD.png" alt="enter image description here"></a></p>