Fixing a bug that was indicated in crash report:

*** -[__NSPlaceholderDictionary initWithObjects:forKeys:count:]: attempt to insert nil object from objects[0]

0
CoreFoundation 0x3443e2a3 __exceptionPreprocess + 163
1
libobjc.A.dylib 0x3c2b297f objc_exception_throw + 31
2
CoreFoundation 0x3438f55f -[__NSPlaceholderDictionary initWithObjects:forKeys:count:] + 135
3
CoreFoundation 0x3438f41b +[NSDictionary dictionaryWithObject:forKey:] + 51
4
PainTracker 0x002585c1 +[TICDSError errorWithCode:underlyingError:userInfo:classAndMethod:] (TICDSError.m:65)
5
PainTracker 0x0025852b +[TICDSError errorWithCode:classAndMethod:] (TICDSError.m:55)
6
PainTracker 0x00278895 -[TICDSDropboxSDKBasedPreSynchronizationOperation restClient:loadedMetadata:] (TICDSDropboxSDKBasedPreSynchronizationOperation.m:158)
7
PainTracker 0x003a221b -[DBRestClient didParseMetadata:] + 75
8
Foundation 0x34d550f5 __NSThreadPerformPerform + 461
9
CoreFoundation 0x34413683 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 15