NSContreteAttributedString：initWithString：崩溃

Question

我想知道可能的原因是什么？ mAutoCommentLabel.text是nil还是cellFont是nil？

UIFont* cellFont = mAutoCommentLabel.font;    
NSAttributedString *attrStr = [[NSAttributedString alloc] initWithString:mAutoCommentLabel.text attributes:@{NSFontAttributeName: cellFont}];

CGRect rect =
[attrStr boundingRectWithSize:CGSizeMake(withWidth, CGFLOAT_MAX)
                             options:(NSStringDrawingUsesLineFragmentOrigin|NSStringDrawingUsesFontLeading)
                             context:nil];

int commentHeight = rect.size.height;

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