//判断是否为空
+(BOOL)IsStringEmptyOrNull:(NSString *)str
{
    if (!str) {
        // null object
        return true;
    }else if (str == nil){
        return true;
    }else {
        if ([str isKindOfClass:[NSNull class]]) {
            return true;
        }else{
            NSString *trimedString = [str stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];
            if ([trimedString length] == 0) {
                // empty string
                return true;
            } else if([trimedString isEqualToString:@"null"]){
                // is neither empty nor null
                return true;
            }
            else if([trimedString isEqualToString:@"(null)"]){
                // is neither empty nor null
                return true;
            }else if([trimedString isEqualToString:@"<null>"]){
                // is neither empty nor null
                return true;
            }else if([trimedString isEqualToString:@""]){
                return true;
                
            }else {
                return false;
            }
        }
    }
}