```
select tupleElement(CAST(tuple(1,2),'Tuple(x UInt64, y UInt64)'), 'x') 
-- ok

select tupleElement(CAST(tuple(1,2),'Tuple(x UInt64, y UInt64)'), 'z')

-- fails
-- Code: 10. DB::Exception: Received from localhost:9000. DB::Exception: Tuple doesn't have element with name 'z': While processing tupleElement(CAST((1, 2), 'Tuple(x UInt64, y UInt64)'), 'z'). (NOT_FOUND_COLUMN_IN_BLOCK)
```
Proposal - add the 3rd parameter to the tupleElement function and return it if tuple doesn't have a member.

Why? Tuple comes from object('JSON'), sometimes some fields are missing in some jsons.
{
    return Tuple(collections::map<Tuple>(elems, [] (const DataTypePtr & elem) { return elem->getDefault(); }));
}
void DataTypeTuple::insertDefaultInto(IColumn & column) const
{
    addElementSafe(elems, column, [&]
    {
        for (const auto & i : collections::range(0, elems.size()))
            elems[i]->insertDefaultInto(extractElementColumn(column, i));
    });
}
bool DataTypeTuple::equals(const IDataType & rhs) const
{
    if (typeid(rhs) != typeid(*this))
        return false;
    const DataTypeTuple & rhs_tuple = static_cast<const DataTypeTuple &>(rhs);
    size_t size = elems.size();
    if (size != rhs_tuple.elems.size())
        return false;
    for (size_t i = 0; i < size; ++i)
        if (!elems[i]->equals(*rhs_tuple.elems[i]) || names[i] != rhs_tuple.names[i])
            return false;
    return true;
}
size_t DataTypeTuple::getPositionByName(const String & name) const