Please update code piece to be:

```php
$identierConstructorCallback = function ($column) { 
    return new Identifier($column); 
};

// ...
$this->_localColumnNames = $localColumnNames 
    ? array_combine($localColumnNames, array_map($identifierConstructorCallback, $localColumnNames)) 
    : array(); 
$this->_foreignColumnNames = $foreignColumnNames 
    ? array_combine($foreignColumnNames, array_map($identifierConstructorCallback, $foreignColumnNames)) 
    : array(); 
```