Nullable cast (?int)

```php
$number = 123; 
(int) $number => 123; 
(?int) $number => 123;

$string = '123'; 
(int) $string => 123; 
(?int) $string => 123;

$null = null; 
(int) $null => 0 
(?int) $null => null
```

See https://externals.io/message/102997