title: -[__NSCFString countByEnumeratingWithState:objects:count:]: unrecognized selector sent to instance
body: <p>I am unable to track down the cause of an IOS crash that keeps popping up. It only happens on the rare occasion to a very small subset of users. I can't follow the crash report back to anything in the app, therefore I didn't post any code. Can anyone help or point me in the right direction?
  Here is the thread reported by crashlytics as being the source of the crash...</p>
  
  <pre><code>Thread : Fatal Exception: NSInvalidArgumentException
  0  CoreFoundation                 0x000000018663c2d8 __exceptionPreprocess + 132
  1  libobjc.A.dylib                0x0000000197c480e4 objc_exception_throw + 60
  2  CoreFoundation                 0x00000001866433a4 __methodDescriptionForSelector
  3  CoreFoundation                 0x0000000186640154 ___forwarding___ + 928
  4  CoreFoundation                 0x0000000186542ccc _CF_forwarding_prep_0 + 92
  5  UIKit                          0x000000018b2d4400 +[_UIDynamicAnimation _updateAnimations:timer:] + 884
  6  QuartzCore                     0x000000018aa1229c CA::Display::DisplayLinkItem::dispatch() + 32
  7  QuartzCore                     0x000000018aa12134 CA::Display::DisplayLink::dispatch_items(unsigned long long, unsigned long long, unsigned long long) + 324
  8  IOKit                          0x00000001877ed470 IODispatchCalloutFromCFMessage + 376
  9  CoreFoundation                 0x00000001865dedc4 __CFMachPortPerform + 180
  10 CoreFoundation                 0x00000001865f3a54 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 56
  11 CoreFoundation                 0x00000001865f39b4 __CFRunLoopDoSource1 + 436
  12 CoreFoundation                 0x00000001865f1934 __CFRunLoopRun + 1640
  13 CoreFoundation                 0x000000018651d2d4 CFRunLoopRunSpecific + 396
  14 GraphicsServices               0x000000018fbf36fc GSEventRunModal + 168
  15 UIKit                          0x000000018b0e2fac UIApplicationMain + 1488
  16 MyAppName                      0x00000001000c8394 main (main.m:7)
  17 libdyld.dylib                  0x00000001982c6a08 start + 4
  </code></pre>
  
  <p>The rest of the threads don't give me a lot more info either.</p>