缩放的时候会闪退

-[NSTaggedPointerString objectForKey:]: unrecognized selector sent to instance 0x8000000000000000

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSTaggedPointerString objectForKey:]: unrecognized selector sent to instance 0x8000000000000000'
*** First throw call stack:
(0x1b180c98c 0x1b15350a4 0x1b171043c 0x1b1810e08 0x1b1812bec 0x1be9c1ab0 0x1031db660 0x1033104bc 0x1033105ac 0x1b5ca35a0 0x1b8190084 0x1b8061c80 0x1b8196a60 0x1b818f960 0x1b81a09b4 0x1b80e99f0 0x1b8113890 0x1b8114284 0x1b1789c48 0x1b1784b34 0x1b1785100 0x1b17848bc 0x1bb5ef328 0x1b58196d4 0x10315db10 0x1b160f460)
libc++abi.dylib: terminating with uncaught exception of type NSException

if let position = kline.volumeMAPositions[ma], let maValue = kline.volumeMAs[ma] 

PKKLineVolumeMAPainter中 47行报错