Acc Create Null Object

Null Object Pattern Generator

Creates Null Object pattern infrastructure for eliminating null checks.

When to Use

Component Characteristics

Interface

• Defines expected behavior
• Shared by real and null implementations
• Enables polymorphic usage

Null Object

• Implements interface with no-op behavior
• Returns neutral values
• Never throws on calls

Benefits

• Eliminates null checks
• Follows Liskov Substitution
• Simplifies client code

Generation Process

Step 1: Generate Interface

Path: src/Domain/{BoundedContext}/

1. {Name}Interface.php — Interface with isNull() method

Step 2: Generate Null Object

Path: src/Domain/{BoundedContext}/

1. Null{Name}.php — Null implementation returning neutral values

Step 3: Generate Real Implementation

Path: src/Domain/{BoundedContext}/

1. {Name}.php — Real implementation with business logic

Step 4: Generate Tests

1. Null{Name}Test.php — Null object behavior tests

File Placement

Naming Conventions

Neutral Return Values

Quick Template Reference

Interface

interface {Name}Interface
{
    public function {method1}(): {returnType1};
    public function {method2}({params}): {returnType2};
    public function isNull(): bool;
}

Null Object

final readonly class Null{Name} implements {Name}Interface
{
    public function {method1}(): {returnType1}
    {
        return {neutralValue1};
    }

    public function isNull(): bool
    {
        return true;
    }
}

Real Implementation

final readonly class {Name} implements {Name}Interface
{
    public function __construct({properties}) {}

    public function {method1}(): {returnType1}
    {
        return {realImplementation};
    }

    public function isNull(): bool
    {
        return false;
    }
}

Usage Example

Repository Returning Null Object

final readonly class DoctrineCustomerRepository implements CustomerRepositoryInterface
{
    public function findById(CustomerId $id): CustomerInterface
    {
        $row = $this->connection->fetchAssociative(
            'SELECT * FROM customers WHERE id = :id',
            ['id' => $id->toString()]
        );

        if ($row === false) {
            return new NullCustomer();
        }

        return $this->hydrate($row);
    }
}

Client Code Without Null Checks

final readonly class CreateOrderUseCase
{
    public function execute(CreateOrderCommand $command): Order
    {
        $customer = $this->customers->findById($command->customerId);

        // No null check needed - NullCustomer returns 0.0
        $discount = $customer->getDiscount();

        $order = Order::create(
            customerId: $customer->id(),
            items: $command->items,
            discount: $discount
        );

        return $order;
    }
}

Anti-patterns to Avoid

References

For complete PHP templates and examples, see:

• references/templates.md — Interface, NullObject, Real Implementation, NullLogger, NullCache templates
• references/examples.md — NullCustomer, NullNotifier, Repository integration examples and tests