SIGSEGV crash

+ (NSString *)getIpByHost:(NSString *)host {
  if ([self isNetworkDelegateState]) {
    OSSLogDebug(@"current network is delegate state");
    return host;
  }
  NSString * ip = [[OSSHttpdns sharedInstance] asynGetIpByHost:host];
  OSSLogDebug(@"resolved host %@ and get ip: %@", host, ip);

  return ip ? [[OSSIPv6Adapter getInstance] handleIpv4Address:ip] : host;
}

libobjc.A.dylib 0x194eff1e0 _NXCompareHashTables + 68
                0x10fe50 +[OSSUtil getIpByHost:]
                0x109a48 -[OSSNetworkingRequestDelegate buildInternalHttpRequest]
                0x10e50c__66 -[OSSTask continueWithExecutor:successBlock:cancellationToken:]_block_invoke
                0x10dd38__59 -[OSSTask continueWithExecutor:block:cancellationToken:]_block_invoke
                0xf3a00__33 +[OSSExecutor defaultExecutor]_block_invoke_2

1. Why it crashes in the getIpByHost method
2. This is an iOS program, where will the _NXCompareHashTables method be called