Null Object Pattern Generator

Creates Null Object pattern infrastructure for eliminating null checks.

When to Use

Scenario	Example
Optional dependencies	Logger, Cache, Notifier
Missing entities	Customer, User, Product
Feature toggles	Disabled feature returns null object
Default implementations	No-op defaults

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

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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

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File Placement

Component	Path
Interface	src/Domain/{BoundedContext}/
Null Object	src/Domain/{BoundedContext}/
Real Implementation	src/Domain/{BoundedContext}/
Unit Tests	tests/Unit/Domain/{BoundedContext}/

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Naming Conventions

Component	Pattern	Example
Interface	{Name}Interface	CustomerInterface
Real Implementation	{Name}	Customer
Null Object	Null{Name}	NullCustomer
Test	{ClassName}Test	NullCustomerTest

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Neutral Return Values

Type	Neutral Value
string	'' (empty string)
int	0
float	0.0
bool	false
array	[]
void	No return
Object	Empty/default instance
Collection	Empty collection

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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;
    }
}

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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;
    }
}

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Anti-patterns to Avoid

Anti-pattern	Problem	Solution
Throwing in Null	Unexpected exceptions	Return neutral values
No isNull()	Can't detect null object	Add isNull method
Different Interface	LSP violation	Same interface as real
Side Effects	Unexpected behavior	Pure no-op methods
Complex Logic	Not a null object	Keep simple and neutral

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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