PHP Nullable Property

class Entity {
    // PHP 7.4+ syntax
    public ?string $shortHandNullable;
    
    // PHP 8.0+ Union Type syntax
    public string|null $unionNullable;
}

class User {
    public ?string $uninitializedName;
    public ?string $initializedName = null;
}

$user = new User();

// Valid: Property was explicitly initialized to null
var_dump($user->initializedName); // Outputs: NULL

// Fatal Error: Typed property User::$uninitializedName must not be accessed before initialization
var_dump($user->uninitializedName); 

class ParentClass {
    public ?string $identifier;
}

class ChildClass extends ParentClass {
    // Fatal error: Type of ChildClass::$identifier must be ?string (as in class ParentClass)
    public string $identifier; 
}