Fix crash in production

*** -[__NSArrayM insertObject:atIndex:]: object cannot be nil
(null)
(
	0   CoreFoundation                      0x2f855feb  + 154
	1   libobjc.A.dylib                     0x3a33accf
objc_exception_throw + 38
	2   CoreFoundation                      0x2f78ff5d
CFStringConvertNSStringEncodingToEncoding + 0
	3   zsh                                 0x268973
-[BFPaperTableViewCell fadeTapCircleOut] + 366
	4   zsh                                 0x265679
-[BFPaperTableViewCell touchesEnded:withEvent:] + 300
	5   UIKit                               0x321f8795  + 232
	6   UIKit                               0x321f8795  + 232
	7   UIKit                               0x320a6721  + 528
	8   UIKit                               0x320a16eb  + 758
	9   UIKit                               0x320768ed  + 196
	10  UIKit                               0x32074f97  + 7102
	11  CoreFoundation                      0x2f82125b  + 14
	12  CoreFoundation                      0x2f82072b  + 206
	13  CoreFoundation                      0x2f81ef1f  + 622
	14  CoreFoundation                      0x2f789f0f
CFRunLoopRunSpecific + 522
	15  CoreFoundation                      0x2f789cf3 CFRunLoopRunInMode
+ 106
	16  GraphicsServices                    0x34683663 GSEventRunModal +
138
	17  UIKit                               0x320d516d UIApplicationMain +
1136
	18  zsh                                 0xe8df7 main + 166
	19  libdyld.dylib                       0x3a847ab7  + 2
)
Merge pull request #2 from yeahdongcn/master

Fix crash in production