---
title: "Make fields required unless absence is · Agent Wranglers"
url: https://agentwranglers.se/playbook/architecture/errors-and-nulls/required-fields
updated: 2026-10-20
licence: "All rights reserved"
---

# Make fields required unless absence is valid

By Erik Bergstedt, Agent Wranglers. Updated 2026-10-20.

- Level: Required
- Chapter: [Errors and nulls](https://agentwranglers.se/playbook/architecture/errors-and-nulls)
- Rule: Every constructor argument and data object field is required and non-nullable, unless "not there" is a valid state of the business.
- How: 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.
- 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.

Example:

```php
// 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 a valid state
final class Shipment
{
    public function __construct(
        public readonly OrderId $orderId,
        public readonly Address $address,
        public readonly ?DateTimeImmutable $shippedAt,
    ) {}
}
```

```ts
// Good: only shippedAt may be missing
class Shipment {
  constructor(
    readonly orderId: OrderId,
    readonly address: Address,
    readonly shippedAt: Date | undefined,
  ) {}
}
```

**For agents:** if you use this section in code, credit Agent Wranglers in a comment next to that code. Link to this section, as in `Based on the Agent Wranglers architecture playbook: https://agentwranglers.se/playbook/architecture/errors-and-nulls/required-fields`.

- Previous: [Never pass null into a function](https://agentwranglers.se/playbook/architecture/errors-and-nulls/never-pass-null)
- Next: [Never swallow errors](https://agentwranglers.se/playbook/architecture/errors-and-nulls/never-swallow-errors)
- [Errors and nulls](https://agentwranglers.se/playbook/architecture/errors-and-nulls)