iOS---字典中的null转换为@“”

+ (NSMutableDictionary *)nullDicToDic:(NSDictionary *)dic{
    
    NSMutableDictionary *resultDic = [@{} mutableCopy];
    if (![dic isKindOfClass:[NSDictionary class]]) {
        return resultDic;
    }
    for (NSString *key in [dic allKeys]) {
        if ([(id)[dic objectForKey:key] isKindOfClass:[NSNull class]]) {
            [resultDic setValue:@"" forKey:key];
        }else{
            [resultDic setValue:[dic objectForKey:key] forKey:key];
        }
    }
    return resultDic;
}