# About using List as the return result, there is null in the problem

**URL:** <https://forum.dfinity.org/t/about-using-list-as-the-return-result-there-is-null-in-the-problem/8279>\
**Category:** Language Support\
**Created:** [November 2, 2021, 9:07am UTC](https://forum.dfinity.org/t/about-using-list-as-the-return-result-there-is-null-in-the-problem/8279 "2021-11-02T09:07:12Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![simpson](https://sea1.discourse-cdn.com/flex023/user_avatar/forum.dfinity.org/simpson/32/10431_2.png) [@simpson](https://forum.dfinity.org/u/simpson)\
**Post date:** [November 2, 2021, 9:07am UTC](https://forum.dfinity.org/t/about-using-list-as-the-return-result-there-is-null-in-the-problem/8279/1 "2021-11-02T09:07:12Z")

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Hello everybody！  
When I use List as the return result, if there are \>1 elements in the List result, then there will be an extra null in the list similar to (opt record {record {status=variant {relate}; owner=principal “rwlgt-iiaaa-aaaaa- aaaaaa-cai”; relateTime=1635842367169199000}; null}), please ask how can I get a clean list, that is, whether there are elements or not, I don’t want a null in it, at least when it is displayed ()

```auto
public shared func getRelates(address:?Text) :async List<ETHRelate>{
        var relateList :?List<ETHRelate> = ethRelates.get(msg.caller);
        var list = Option.get<List<ETHRelate>>(relateList,List.nil<ETHRelate>());
        if (address != null){
            var list = List.nil<ETHRelate>();
            List.iterate<ETHRelate>(list,func(obj:ETHRelate){
                if (?obj.address == address){
                    list := List.push<ETHRelate>(obj,list);
                };
            });
            return list;
        } else {
            return list;
        };
    };

(opt record {record {status=variant {relate}; owner=principal "rwlgt-iiaaa-aaaaa-aaaaa-cai"; relateTime=1635842367169199000; address="0x6865fC780d3267CE0F13d95eb8ec82b768C99475"; unRelateTime=null}; null})

```

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<div class="post-metadata">

**Author:** ![nomeata](https://sea1.discourse-cdn.com/flex023/user_avatar/forum.dfinity.org/nomeata/32/733_2.png) [@nomeata](https://forum.dfinity.org/u/nomeata)\
**Post date:** [November 2, 2021, 9:11am UTC](https://forum.dfinity.org/t/about-using-list-as-the-return-result-there-is-null-in-the-problem/8279/2 "2021-11-02T09:11:19Z")

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The `List` type is defined as

```auto
type List<T> = ?(T, List<T>)

```

so it is always terminated with a `null` value.

It is not a great type for public interfaces, I suggest to use arrays in the public interface (so use return type `async [ETHRelate]` and `return list.toArray()`), as this maps to Candid’s `vec` type, which is what users of your interface will likely expect.

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**Author:** ![simpson](https://sea1.discourse-cdn.com/flex023/user_avatar/forum.dfinity.org/simpson/32/10431_2.png) [@simpson](https://forum.dfinity.org/u/simpson)\
**Post date:** [November 2, 2021, 9:12am UTC](https://forum.dfinity.org/t/about-using-list-as-the-return-result-there-is-null-in-the-problem/8279/3 "2021-11-02T09:12:58Z")

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I agree with you, thank you very much