1. Application Specific Information:
   *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[__NSCFString rangeOfString:options:range:locale:]: nil argument'

solution：
情形一：str 不能为nil， 需进行判空处理，否则当str == nil，是就会crash, 注意containsString 是iOS8中才出现的API，所以在小于iOS8的系统中运行也将导致程序崩溃

NSString method "containsString:" 

/// str must not be nil. 
-(BOOL)containsString:(NSString *)str;

情形二：searchString 不能为nil， 需进行判空处理，否则当searchString == nil，是就会crash,

NSString method "rangeOfString:" 

/// searchString must not be nil. 
- (NSRange)rangeOfString:(NSString *)searchString;