SWIFT：错误“线程1：EXC_BAD_INSTRUCTION（代码= EXC_I386_INVOP，子代码= 0x0）”是什么意思？

我得到这个错误，我该如何解决这个错误？ 当我运行应用程序崩溃。 它给出了这个错误，任何人都可以帮忙？ 提前致谢。

错误在于： let initialAttitude = manager.deviceMotion!.attitude

 // get magnitude of vector via Pythagorean theorem func magnitudeFromAttitude(attitude: CMAttitude) -> Double { return sqrt(pow(attitude.roll, 2) + pow(attitude.yaw, 2) + pow(attitude.pitch, 2)) } // initial configuration let initialAttitude = manager.deviceMotion!.attitude //THIS IS THE LINE OF CODE WITH THE ERROR var showingPrompt = false // trigger values - a gap so there isn't a flicker zone let showPromptTrigger = 1.0 let showAnswerTrigger = 0.8 if manager.deviceMotionAvailable { manager.startDeviceMotionUpdatesToQueue(NSOperationQueue.mainQueue()) { [weak self] (data: CMDeviceMotion?, error: NSError?) in guard let data = data else { return }