Make fields required unless absence is real

How to do it

Ask for each optional field what it means when it is empty. If it is always set in practice, make it required. If absence has a meaning, such as "not shipped yet", name that state with its own type or an optional field. Build objects fully in the constructor, never half-filled with setters.

Example

// Bad: everything is nullable, so nothing can be trusted
final class Shipment
{
    public function __construct(
        public ?string $orderId = null,
        public ?string $address = null,
        public ?DateTimeImmutable $shippedAt = null,
    ) {}
}

// Good: only shippedAt may be missing, because "not shipped yet" is real
final class Shipment
{
    public function __construct(
        public readonly OrderId $orderId,
        public readonly Address $address,
        public readonly ?DateTimeImmutable $shippedAt,
    ) {}
}

How to check

A type checker rejects missing fields, such as TypeScript strict, PHPStan level max or mypy --strict. Reviewers fail any nullable field that no code path ever leaves empty.