我遇到了一个崩溃的关联AVSpeechSynthersizer。 我的代码是，
AVSpeechUtterance *utterance = [[AVSpeechUtterance alloc] initWithString:text];
utterance.rate = rate;
utterance.pitchMultiplier = pitchMultiplier;
utterance.voice = [AVSpeechSynthesisVoice voiceWithLanguage:languageCode];
_startTime = [[NSDate date] timeIntervalSince1970];
[self.speechSynthesizer speakUtterance:utterance];
此崩溃只有一个用户案例。操作系统版本为11.4，设备为iPhone6。
崩溃堆栈信息：
Incident Identifier: 24E003DC-47C0-45B0-A22E-A351B2A8046A
CrashReporter Key: c8844c975fe64b90aad2b813254959a928e4c4ea
Hardware Model: iPhone7,2
Process: qcs.r [779]
Path: /var/containers/Bundle/Application/0242C042-0AE5-4033-AE07-D1BECD6DD910/qcs.r.app/qcs.r
Identifier: com.meituan.qcs.r.ios
Version: 2.1.9 (1682)
Code Type: ARM-64
Parent Process: ? [1]
Date/Time: 2018-06-14 13:41:58.000 +0800
OS Version: iOS 11.4 (15F79)
Report Version: 104
Exception Type: EXC_CRASH (SIGABRT)
Exception Codes: 0x00000000 at 0x0000000000000000
Crashed Thread: 53
Application Specific Information:
*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** +[NSString stringWithUTF8String:]: NULL cString
UserInfo:(null)'
Thread 53 Crashed:
0 CoreFoundation __exceptionPreprocess+ 228
1 libobjc.A.dylib objc_exception_throw (in libobjc.A.dylib) + 56
2 CoreFoundation -[NSException initWithCoder:]+ 0
3 Foundation +[NSString stringWithUTF8String:]+ 92
4 TTSSpeechBundle 0x0000000105f87544 0x105f70000 + 95556
5 libsystem_pthread.dylib _pthread_body (in libsystem_pthread.dylib) + 272
6 libsystem_pthread.dylib _pthread_body (in libsystem_pthread.dylib) + 0
7 libsystem_pthread.dylib thread_start (in libsystem_pthread.dylib) + 4
你这里的文本参数会不会是零？ initWithString：text