从NSMutableData中移除字节

NSMutableData对象中移除最末六位的字节，对象如下：

NSMutableData *reducedDataPacket = [[NSMutableData alloc] init];
        reducedDataPacket = [myCompressedData copy];

NSRange range = NSMakeRange([reducedDataPacket length]-6, 6);
        [reducedDataPacket replaceBytesInRange:range withBytes:NULL length:0];

但是执行会引发崩溃：

-[NSConcreteData replaceBytesInRange:withBytes:length:]: unrecognized selector sent to instance 0x1f037870
Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSConcreteData replaceBytesInRange:withBytes:length:]: unrecognized selector sent to instance 0x1f037870

感谢您的回答！

你好 请问您这个问题解决了没有？因为我现在也遇到一样的问题，不知道怎么调试，请帮忙提示下 谢谢。