sbjson解析出的json字符串包含null时的处理方法

            id friend_nick = [friends[i] objectForKey:@"friend_nick"];
            //NSLog(@"friend_nick = %@",friend_nick);
            
            if ([friend_nick isKindOfClass:[NSNull class]]) {
                //处理，填写替换字符串
                friend.friend_nick = @"替换字符";
            }