For example Null can be represented as empty string

```sql
select arrayStringConcat(['x',Null], ';');

┌─arrayStringConcat(['x', Null], ';')─┐
│ x;                                  │
└─────────────────────────────────────┘
```

But mostly it for avoiding a cast in case of Nullable Strings
```
SELECT arrayStringConcat(col0, ';')
FROM
(
    SELECT [toNullable('x')] AS col0
) AS t
```

Also I think arrayStringConcat can support any types not only Strings, it allows to avoid explicit casts.

```
SELECT arrayStringConcat(col0, ';')
FROM
(
    SELECT [1, 2, 3] AS col0
) AS t
```
#pragma once
#include <Columns/ColumnArray.h>
#include <Columns/ColumnConst.h>
#include <Columns/ColumnFixedString.h>
#include <Columns/ColumnNullable.h>
#include <Columns/ColumnString.h>
#include <DataTypes/DataTypeArray.h>
#include <DataTypes/DataTypeNullable.h>
#include <DataTypes/DataTypeString.h>
#include <Functions/FunctionHelpers.h>
#include <Functions/IFunction.h>
#include <Functions/Regexps.h>
#include <IO/WriteHelpers.h>
#include <Interpreters/Context_fwd.h>
#include <Common/StringUtils/StringUtils.h>
#include <Common/assert_cast.h>
#include <Common/typeid_cast.h>
namespace DB
{