I am running instruments via Terminal:

```
instruments -t /Developer/Platforms/"iPhoneOS.platform/Developer/Library/Instruments/PlugIns/Au‌​tomationInstrument.bundle/Contents/Resources/Automation.tracetemplate ~/Library/Application\\\ Support/iPhone\\\ Simulator/$simulatorSDKVersion/Applications/<randomUUID>/MyApp.app -e UIASCRIPT someJSFile.js -e UIARESULTSPATH Logs

```

for several test scripts. 

But I keep getting sporadic crashes and this is interfering with the workflow I have set up. 

Can anyone tell me what this means:

```
instruments[57679:1603] InstrumentsException : *** -[__NSCFString stringByAppendingString:]: nil argument
instruments[57679:1603] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[__NSCFString stringByAppendingString:]: nil argument'
*** First throw call stack:
(
    0   CoreFoundation                      0x00007fff90ed4f56 __exceptionPreprocess + 198
    1   libobjc.A.dylib                     0x00007fff90598d5e objc_exception_throw + 43
    2   CoreFoundation                      0x00007fff90ed4d8a +[NSException raise:format:arguments:] + 106
    3   CoreFoundation                      0x00007fff90ed4d14 +[NSException raise:format:] + 116
    4   Foundation                          0x00007fff939e9375 -[NSString stringByAppendingString:] + 91
    5   AutomationInstrument                0x000000010c5b6695 AutomationInstrument + 30357
    6   libdispatch.dylib                   0x00007fff8ad07a86 _dispatch_call_block_and_release + 18
    7   libdispatch.dylib                   0x00007fff8ad098f6 _dispatch_main_queue_callback_4CF + 308
    8   CoreFoundation                      0x00007fff90e69e7c __CFRunLoopRun + 1724
    9   CoreFoundation                      0x00007fff90e69486 CFRunLoopRunSpecific + 230
    10  Foundation                          0x00007fff939d7f7b -[NSRunLoop(NSRunLoop) runMode:beforeDate:] + 267
    11  Foundation                          0x00007fff93a5bb56 -[NSRunLoop(NSRunLoop) runUntilDate:] + 66
    12  instruments                         0x00000001091d03c1 _mh_execute_header + 13249
    13  instruments                         0x00000001091ce194 _mh_execute_header + 4500
)
terminate called throwing an exception

```

Thanks!

P.S. Not sure if this is the right site to post this question on.